Between 1980 and 1985, 6067 out-patient vasectomies were performed under local anaesthesia at the Elliot Smith Clinic in Oxford. During this period 151 men (2.5%) were given a "special clearance". This sanctioned the discontinuation of other forms of contraception despite the persistence of scanty (less than 10,000/ml) sperm in 2 consecutively examined semen samples at least 7 months after vasectomy. These men have been reviewed and further specimens of semen requested after a minimum follow-up of 3 years (range 3-8); 50 patients supplied a specimen and all except 1 were azoospermic. No pregnancies attributable to failure of the vasectomy have been identified.