The study had a case-control design, Cases were women hospitalized with MI or stroke in any of nine participating Northern California Kaiser Permanente hospitals in a 36 month period. For each case, one control, matched by year of birth, was selected at random from among members of the Kaiser Permanente Health Plan who were expected to use the same nine hospitals for their medical care. Information about use of estrogen, E/P combinations, past use of oral contraceptives, menopause, hysterectomy and oophorectomy, demographics, general health status, preventive health care, and cardiovascular risk factors were collected in interviews done of the subjects or, for fatal cases, a surrogate. Information about then current use of estrogen and E/P combinations were also gathered by reviewing medical records.