A cross-sectional study of 216 impotent men aged 40 to 79 years (mean age 60.9 years) was conducted to determine if there are age-related changes in clinical and hormonal parameters in an impotent population. There was a slight increase in the degree of sexual dysfunction with age, with complete erectile failure occurring in a larger percent of the 60- and 70-year-olds than in the younger patients (41% vs 27% for the 40 year olds, P less than .05). No patient above the age of 70 years reported any full erections, even of short duration. In contrast, reported levels of libido did not vary significantly with age. Abnormal penile Doppler studies diagnostic of vasculogenic impotence were found in 17.8% of the patients tested, and an additional 17.8% were found to have evidence suggestive of a vascular etiology. These abnormal vascular findings were associated with an extremely high prevalence of clinically apparent atherosclerosis in this population. In 22.9% of the subjects, an abnormal vascular response was found only on exercise, ie, a "pelvic steal", which only occurred above the age of 50 years. There was a marked age-related alteration in the concentration of testosterone (T) and bioavailable testosterone (BT), but no statistically significant change in the levels of gonadotropins with age. An increase in the prevalence of eugonadotropic hypogonadism with age was found, which suggested an increasing prevalence of hypothalamic pituitary dysfunction in this patient group. For both vascular and hormonal changes (such as low T and BT), the greatest changes appear to occur after the age of 50.(ABSTRACT TRUNCATED AT 250 WORDS)