The prospective study addressed the impact of weight fluctuation on development of hypertension (HPT) and diabetes (DM) by following women who significantly fluctuated in weight compared to those who generally maintained a stable weight. The subject source was all participants between 1989 and 1993 in the Nurses Health Study II (NHS) who did not experience a full term pregnancy between 1989 and 1993 and who were free of HPT, DM and cancer in 1993. A random sample of each of two weight fluctuation classifications, >20 lbs. (3 or more times) and 10-19 lbs. (3 or more times) was identified. A control group of non-fluctuators was matched by age and body mass index strata. Baseline data consisted of information obtained from the 1993 NHS II follow-up along with supplemental questionnaires sent to study participants to elicit specific information on past and present weight gain/loss and intentionality of weight fluctuation. Prospective data came from follow-up questionnaires in 1995, 1997, and 1999. Hypertension and DM ascertainment were obtained from self-report in the questionnaire. This ascertainment method appeared quite adequate based on validity studies carried out on subsamples of this cohort.