Erectile dysfunction (ED) seriously impairs the quality of life. Patients with diabetes mellitus (DM) are prone to ED due to various factors, including vasculopathy, neuropathy and sex hormone abnormalities. This is a retrospective study involving 1,511 patients taking sildenafil. Patients with DM have significantly more comorbidities like hypertension and ischaemic heart disease. They are also more likely to be on medications which may affect erectile function, including various antihypertensive drugs. 77.9% of patients with DM reported success with sildenafil, as compared to 86.5% of patients without DM. A significant number of patients with DM require a higher dose of sildenafil as compared to those without DM.