Inflow cystometry and the pressure flow analysis of micturition were performed on 100 male patients (ages 47–85) before, and 4 months after, prostatic surgery for benign prostatic enlargement. Symptomatic improvement was noted in 88% and the objective relief of obstruction in 93%. Persistent symptoms were seen in 12% of patients and were due to persistent obstruction, to bladder hypersensitivity or to bladder instability. As bladder hypersensitivity or instability may produce a symptom complex identical to that seen in outflow obstruction, it is recommended that objective evidence of obstruction should be sought prior to any surgery aimed at its relief.