Chromium is one of the toxic heavy metals, which is extensively discharged from tanning industry to the environment. Chromium has binding potential to biomolecules in living systems and cause toxicity to biological life. Leather industry has been categorized as one of the highly polluting industry. Tanning industry is polluting the environment at a higher rate with huge amount of harmful material. These pollutants are also harmful for environment, humans and aquatic organisms. The aim of the present study was to investigate the effects of chromium on selected endocrine hormones, oxidative stress, DNA damage, biochemical and haematological parameters of tannery workers and environmental parameters. Two major cities, Peshawar and Sheikhupura, were selected for the sampling sites. Samples of effluents, ground water, soil and vegetables were collected from the neighboring vicinity of tanning industries. The background area and adjoining villages were considered as control areas. Seven trace metals (Cr, Cu, Ni, Cd, Pb, Fe, and Zn) were investigated in tannery effluents, ground water, soil and dietary vegetables (Spinacia oleracea, Solanum tuberusom and Solanum melongena) samples using Graphite Furnace Atomic Absorption Spectrophotometer. It was observed that both soil and groundwater of study area were badly affected by the toxic elements discharged by tanning industries. The maximum level of Cr in tannery effluents was 350.15 mg/l, while in the soil sample it approached to 31.13mg/l. The values of chromium, cobalt, cadmium, lead and iron in the tannery effluents from Sheikhupura and Peshawar were above the permissible limits set by WHO (World health organization) and FAO (Food and Agriculture organization). The concentration of chromium, cadmium, nickel and lead in study area ground water from Sheikhupura and Peshawar exceeded the standards of NSDWQ/Pak (National standard for drinking water quality). Vegetables irrigated with tannery effluents showed elevated level of Cr, Zn, Ni and Cd, which were above the permissible limits of WHO/FO. There was a significant positive correlation between all the trace metals in three media, tannery effluent, soil and ground water (p<0.001). The metal to metal association was supported by dendrograms using cluster analysis. A total of 240 smoking and nonsmoking individuals were registered in the study, including 120 chromium exposed tannery workers and 120 controls. The workers were selected from the tanneries of Sheikhupura and Peshawar, Pakistan. The average age of exposure group I was 20-35 years, exposure group II was 36-50 years and controls were 20-50 years. Hormonal parameters in the blood samples were determined by commercial kit, Chemiluminescent Microparticle Immunoassay (CMIA). Oxidative stress parameters were measured in the blood samples by spectrophotometric methods. DNA damage in lymphocytes was measured by comet assay (single-cell gel electrophoresis). Blood samples were collected from different age group subjects (chromium exposed tannery workers and controls). The results revealed that both smoking and nonsmoking exposed groups showed significantly higher chromium levels in blood and urine than those of unexposed groups. The levels of testosterone (326.238± 12), (306.636±13.8) and growth hormones (0.1030±0.03), (0.0734±0.01) were significantly decreased in both age groups of male tannery workers exposed to chromium. The level of progesterone (2.416 ± 1.1), estradiol (48.879 ± 40.1), luteinizing (1.9692± 0.82) and growth hormones of female tannery workers (0.7983±0.1) were significantly decreased while follicle stimulating hormone (9.2857 ± 0.7) was significantly increased as compared to unexposed population. Thyroid stimulating hormone, triiodothyronine and tetraiodothyronine hormones were not affected in tannery workers. The hormones in tannery workers in group II aged (36-50) were more affected due to long-term Cr exposure as compared to group 1 with short term chromium exposure and controls. This was further supported by correlation and regression analyses of the data. Pearson correlation showed that the levels of sex hormones (testosterone, progesterone, estradiol and luteinizing hormone) and growth hormone had negative correlation with blood chromium concentration in tannery workers. The present study revealed that occupational exposure to Cr (VI) and Cr (III) can lead to a detectable DNA damage in tannery workers. DNA damage (28.79± 2.154), (25.41± 7.199) in smoking and nonsmoking tannery workers were significantly higher than those of unexposed groups. In addition, DNA damage was significantly associated with concentration of chromium in blood. Malondialdehyde (MDA) levels (11.00 ± 0.7), (8.77± 2.3) and superoxide dismutase (SOD) concentrations (75.178± 2.3), (79.52±1.9) of smoking and nonsmoking exposed groups were significantly higher than those of unexposed groups. While glutathione (GSH) levels (59.926 ± 1.5), (55.702 ± 2.3) in smoking and nonsmoking exposed groups were significantly lower when compared with unexposed groups. Oxidative stress parameters and DNA damage in group II tannery workers aged (36- 50) with long-term Cr exposure were more affected as compared to tannery workers in group I with short term chromium exposure and controls. This investigation was further supported by correlation analysis. There was positive correlation between levels of blood chromium and DNA damage, MDA and SOD levels, while negative correlation was observed between blood chromium concentration and GSH levels in tannery workers. The results showed that duration of exposure and smoking has significant effect on DNA damage and oxidative stress parameters in tannery workers. The present study also described biochemical and haematological defects in tannery workers exposed to hexavalent chromium. From the findings, it is evident that white blood cells (WBC) (8.373±0.7), red blood cells (RBC) (4.12±0.5), haemoglobin (Hb) (10.02±1.14), mean corpuscular haemoglobin (MCH) (25.91±1.50), and packed cell volume (PCV) (42.62±2.0) were lower in exposed groups than that of controls. The values of liver function tests of tannery workers were found to be within the normal range in both the age groups except alkaline phosphatase (AP) activity (121.28±8.3), which was significantly increased in exposed groups. All other biochemical parameters were found to be within the normal range except the albumin (Alb) levels which was significantly decreased in exposed groups. The present study found that occupational exposure to chromium can lead to health hazards including hormonal abnormalities, oxidative stress, DNA damage and hematological and biochemical defects in tannery workers.