Many studies indicate that women live longer than men but report more physical illness. This report is the first prospective study of sex ratios for morbidity and mortality due to a variety of causes in a single cohort: a random sample of 5,239 adults, aged 30 years or older in 1965, who have been followed through 1983 (19 years) by cause and age. For both cancer incidence and mortality there was a female excess before age 50 years, followed by a male excess peaking between ages 60 and 69 years. Sex ratios for ischemic heart disease mortality, on the other hand, indicated a male excess at virtually all ages, and that these sex ratios declined with age. However, three measures of heart disease morbidity (self-reported chest pain, heart trouble, and high blood pressure) demonstrated a female excess that did not vary by age. All four measures of functional disability (impaired self-care, impaired mobility, cessation of work, and reduction of work) demonstrated a female excess that did not vary by age (with the exception of a male excess in impaired self-care in adults aged 30 to 39 years). Further analyses of sex differences in health need to acknowledge the heterogeneity of the relation of sex to disease, and the complex age-sex interaction that varies remarkably with both cause and manifestation of outcome (morbidity vs. mortality).