Nonarteritic anterior ischemic optic neuropathy (NAION) has been reported rarely in men after taking sildenafil or other phosphodiesterase 5 inhibitors for erectile dysfunction (ED). The incidence of NAION in men receiving sildenafil treatment for ED was estimated using pooled safety data from global clinical trials and European observational studies. Based on clinical trial data in more than 13,000 men and on more than 35,000 patient-years of observation in epidemiologic studies, we estimated an incidence of 2.8 cases of NAION per 100,000 patient-years of sildenafil exposure. This is similar to estimates reported in general US population samples (2.52 and 11.8 cases per 100,000 men aged >or=50 years). The data cited herein do not suggest an increased incidence of NAION in men who took sildenafil for ED.