It is known that a proportion of patients who undergo transurethral resection of the prostate (TURP) will develop erectile dysfunction (ED). This study examined the incidence of ED after TURP using objective and subjective parameters and risk factors for the development of ED. All benign prostate hyperplasia (BPH) patients who were indicated for TURP had to meet the criteria of the International Index of Erectile Function (IIEF) 5 scores of more than 16, and with normal nocturnal penile tumescense (NPT) which had at least one episode of nocturnal erections with both base and tip rigidity exceeding 55% for at least 10 min. The patient's nocturnal erection were measured using Rigiscan, over two consecutive nights, approximately 3-4 days preoperatively and 3 months postoperatively. A total of 63 patients were eligible for the study; the mean age was 63.3 years (range 49-85 years). Nine (14%) patients were found to have postoperative ED. Patients who developed ED postoperatively had a lower IIEF-5 score and NPT parameters preoperatively (for all parameters, P<0.0001). For risk factors, diabetes mellitus were found to be a significant independent risk factor. The incidence of ED post-TURP using objective parameters was 14%. Without taking note of the risk factors, TURP is a safe procedure with regard to sexual function.