Although subgroup analyses from large randomised premarketing studies have shown that Apomorphine SL enhances the percentage of erections firm enough for sexual intercourse in diabetic men, the clinical role of the drug in this patient population remains to be elucidated. The aim of the present study was to assess the efficacy of Apomorphine SL in diabetic males with erectile dysfunction (ED) and to identify factors predicting those who may benefit from the treatment. A total of 130 diabetic patients were randomised to receive either four tablets of 3 mg Apomorphine or a matching placebo. Assessments of efficacy comprised the erectile function (EF) domain of the International Index of Erectile Function (IIEF) and the one-item global efficacy question (GEQ). Patients with both a positive response to the GEQ and an improvement of at least 5 points in the EF domain of the IIEF were considered responders and subanalysed by several parameters indicative of the severity of both ED and diabetes. Response rate was 17% after placebo and 22% after Apomorphine SL. The EF domain of the IIEF and both questions 3 and 4 scores did not significantly improve in either of the two arms over the baseline. A younger age and a lower Hb1Ac were significantly linked to the status of responder in the Apomorphine arm. Apomorphine SL failed to show a statistically significant benefit over a placebo, but 22% of patients had a clinically significant erectile response. These figures seem to suggest that the drug has a limited use for ED diabetic patients.