Sexual behaviour after prostatectomy has been observed in 100 patients who have undergone a Millin prostatectomy with preventive haemostasis. The results have been compared with 100 patients subjected to other urological operations and 100 patients who have undergone general surgical operations. From the data obtained we conclude that: (1) one third of the patients who have undergone prostatectomy no longer have sexual activity; (2) prostatectomy does not affect sexual potency more than any other operation of the same gravity at the same age; (3) among the patients sexually active 6 months before prostatectomy, 45% have a better sexual life 6 months afterwards, 26% have a diminished sexual life and 3.5% have become impotent; (4) the development of an adenoma seems to have an unfavourable influence on sexual activity.