From May 1986 to January 1989, a total of 178 patients with small prostate (less than 20 grams) received transurethral resection for benign prostatic hyperplasia. Twenty-two patients (12.4%) developed bladder neck contracture with an average interval of 247 days. The prophylactic bladder neck incision was performed concomitantly with transurethral resection of the prostate on 72 patients. Although smaller adenoma (average weight: 11.4 grams) was resected in this group, the bladder neck contracture occurred in 4 patients (5.6%), compared to 18 contractures in 106 patients (16.9%) who underwent transurethral resection of the prostate alone for larger adenoma (14 grams), P value less than 0.05. The operation time, peri-operative morbidity and hospital stay were similar in these two groups. It appeared that prophylactic bladder neck incision could protect against the formation of bladder neck contracture in patients with small obstructing prostatic adenoma.