Erectile dysfunction (ED) represents an important quality-of-life issue for many ageing men. Low serum testosterone level and other factors may be involved. Sildenafil is effective and well tolerated in patients with ED of various aetiologies, showing an efficacy of about 75%. However, few efficacy and adverse effect studies have focused specially on ageing men. In 150 patients below 65 years and 44 patients over 65 years, sildenafil was used to treat ED. Efficacy in the younger group (89.1%) was greater than in the older group (65.7%; p < 0.01). Mean serum luteinizing hormone (LH) and follicle-stimulating hormone concentrations (11.0 and 18.9 mIU/mL, respectively) in the older group were higher than in younger group (5.2 and 8.7 mIU/mL, respectively; p < 0.01). Serum testosterone and prolactin (PRL) were similar between groups. Older patients showed higher prevalence of diabetes mellitus, hypertension, and benign prostatic hyperplasia. Only diabetes appeared to decrease efficacy of sildenafil in older patients (p=0.019). A high prevalence of diabetes might be one of the many causes of lower efficacy rate of sildenafil in older men, although efficacy in patients even without diabetes in older men was relatively low. Sildenafil can be used safely and it is still effective for ageing male, because nearly two-thirds of our older subjects had a good response to the drug and no adverse effect was specific to older patients.