Introduction: Acute kidney failure (acute kidney injury, AKI) is a group of syndromes that result in a decline in the glomerular filtration rate. In 2002, the Acute Dialysis Quality Initiative (ADQI) group proposed the RIFLE criteria to standardize the definitions of AKI severity and outcome. This criterion has been validated in several studies. AKI is frequently encountered in hospitalized patients; it has a negative impact on mortality and morbidity. A lot of work has been done to describe the epidemiology of AKI in developed countries. The same does not apply for developing countries. This study was designed to evaluate AKI in a tertiary care hospital in Nairobi, Kenya. Objectives: This study was designed to determine the period prevalence of acute renal failure in all patients admitted to the hospital during the study period, to determine the severity of acute renal failure in these patients based on the RIFLE criteria and to elucidate the associated risk factors leading to renal failure in the patients. We also described the modalities used to manage the patients as well as their outcome at the time they were leaving hospital Method: We carried out a prospective cross sectional study to determine the epidemiology of acute kidney injury in a tertiary care hospital in Kenya. All patients over the age of 12 years admitted to the hospital were followed up prospectively and those diagnosed to have AKI at any time during their stay in hospital were assessed for risk factors, mode of management and outcome. Results: A total of 102 patients were enrolled during the study period running from 1st April 2007 to 31st December 2007. The period prevalence was found to be 1050 per 100000. Other studies have found a prevalence ranging from 400 to 5700 per 100000. Higher values were found in the critical care areas. Seventy one (69.9%) of the patients were male, 81(80%) were African and the mean age of the cohort was 50.1 years. We found that 41(40%) of the patients were in the failure category while risk and injury constituted 27(26%) and 34 (34%) respectively. The commonest risk factor was drug use especially angiotensin converting enzyme inhibitors (23.81%), non steroidal anti-inflammatory drugs (14.29%), anti retroviral drugs (19.05% and diuretics (9.52%). Other commonly associated findings included a history of vomiting, diarrhea and seizures. The most common underlying diagnoses were sepsis (50%), diabetes mellitus (34.31), malignancies (25.49%), surgical (24.49%) and pulmonary diseases