87 cases of urethral stenosis were treated over a two year period. This study was motivated by the high incidence of urethral stenosis after cardiac surgery. The patients were classified into four groups; urological surgery, cardiovascular surgery, medicine and other surgical specialties. The mean age was 60. It is easy to explain the development of urethral stenosis following endoscopic urological surgery, but rather more difficult, following cardiac surgery. The patients undergoing cardiac surgery were compared with those having a transurethral resection of the prostate. Neither traumatic catheterisation, urinary infection, prolonged catheterisation nor any factors specific to cardiac surgery could be implicated. The number of stenoses of the penile urethra was similar to the number of stenoses in the bulbar urethra. The critical period is within the first three months following surgery. Two hypotheses have been proposed to explain the pathogenesis of urethral stenosis after cardiac surgery: a hypersensitivity of the urethral mucosa combined, perhaps, with episodes of ischaemia. In order to verify the first hypothesis, the authors undertook a prospective study. Two groups of patients were chosen at random: 45 had a urethral catheter, 28 had a cystocatheter; 4 cases of urethral stenosis developed after the urethral catheter and there were no cases with the cystocatheter.