Introduction: We report the methodology and results of a study that compared a dopaminergic agonist, apomorphine, with a phosphodiesterase type-5 inhibitor, sildenafil, in terms of efficacy, tolerability, satisfaction and patient preference. Patients and Methods: This was a 20-week open- label, randomized, flexible-dose, crossover study to assess the comparative efficacy and safety of sildenafil and apomorphine. One sequence group received treatment with sildenafil followed by apomorphine and the other sequence group received treatment with apomorphine followed by sildenafil. The primary efficacy variable was the measurement of the score of the erectile function domain (the sum of questions 1–5 and 15) of the International Index of Erectile Function (IIEF) questionnaire. The secondary efficacy variables were: the responses to the Global Efficacy Assessment Questions; the score of the responses to all the questions of the IIEF questionnaire; the index score of the Erectile Dysfunction Inventory of Treatment Satisfaction questionnaire, and the event log variables. Results and Conclusions: A marked increase in the mean IIEF score was observed after treatment with sildenafil, compared with a small increase following treatment with apomorphine. The mean baseline and final scores before and after treatment with sildenafil were 13.9 ± 5.2 and 24.1 ± 5.2, while the corresponding mean scores before and after treatment with apomorphine were 14.2 ± 5.1 and 16.8 ± 6.2. The comparison between treatments showed a statistically significant difference in favor of sildenafil. Furthermore, sildenafil was found to be significantly superior to apomorphine in all the other secondary variables, produced a high level of patient satisfaction, and a significantly larger number of patients indicated their preference for sildenafil compared to apomorphine.