Background: Men with lower urinary tract symptoms (LUTS) are at risk of erectile dysfunction (ED) and other co - morbidities. The clinical assessment of ED is unreliable and the International Index of Erectile Function – 5 (IIEF – 5) a widely used tool is not validated in our setting. We aimed to validate the IIEF – 5 as a screening tool for ED in men with LUTS visiting the outpatient services. Methodology: In the study, 99 men above 40 years with LUTS attending the urology clinics were consecutively enrolled, administered with the IIEF – 5 and assigned an ED status. Socio – demographic data and risk factors were captured in a separate questionnaire. A blinded urologist made an independent clinical assessment of ED following this. Results: In this study involving 99 men with LUTS, 45.5% had mild ED, 24.2% had no ED, 17.2% had mild-moderate ED, while 13.1% had moderate ED based on IIEF – 5 score. In comparison, 84.8% had no ED and 15.2% had ED based on clinical assessment. The questionnaire items were very correlated as determined by a Cronbach's alpha of 0.920. Determination of ceiling and floor effects was based on a cutoff of at least 15% of patients obtaining the least points of 5/25 for the floor effect or best points of 25/25 for the ceiling effect. 7.1% of patients scored 25/25 and none scored 5/25 hence no ceiling or floor effect was observed. The area under the curve 0.884 (p = 0.000002) demonstrated good diagnostic performance with favourable sensitivity and specificity. Conclusion: For men above 40 years with LUTS, the IIEF-5 is a valid and reliable tool to screen for ED. These results, taken with results from previous validation studies of the IIEF – 5 suggest that it should complement clinical assessment of ED.