The usefulness of nocturnal penile tumescence (NPT) monitoring with stamps was evaluated in diabetic males with impotence. The stamps, which were similar in paper and size to Japanese 10-yen postage stamps, were wrapped around the penis before sleep and the stamp ring was checked for breakage the next morning. Clinical features of the subjects were investigated by penile blood pressure index (PBPI), neurological examinations, psychological tests, and hormonal measurements. Nineteen out of 37 patients with impotence had a breakage of the stamp rings on one or more of 3 nights. The patients with non-breakage of stamp rings had significantly more serious diabetic neuropathy (peripheral and autonomic), depressive tendency, loss of libido, and a higher prevalence of heavy smoking than those with breakage of the stamp rings. PBPI and hormonal findings showed no difference between the breakage and non-breakage patients. These results show that the diagnostic value of this method is nearly the same as that of NPT recording with a strain gauge.