OBJECTIVE: The aim of this study was to examine the associations of demographic characteristics, health behaviors, and hormone concentrations with the experience of any, current, more severe, and more frequent midlife hot flashes. METHODS: Baseline data from 732 women aged 45 to 54 years who were enrolled in the Midlife Women's Health Study were analyzed. A clinic visit was conducted to collect blood samples for hormone assays and to measure ovarian volume using transvaginal ultrasound. A self-administered questionnaire ascertained information on demographic factors, health habits, and hot flash history. Multivariable logistic regression was conducted to examine associations between potential risk factors and hot flash outcomes. RESULTS: Approximately 45% of participants reported experiencing midlife hot flashes. In covariate-adjusted models, older age, perimenopause status, current and past cigarette smoking, and depressive symptoms were significantly associated with increased odds of all of the hot flash outcomes. In addition, history of oral contraceptive use was associated with increased odds of any hot flashes. In contrast, higher current alcohol intake was significantly associated with decreased odds of any, current, and more severe hot flashes. Higher estradiol and progesterone concentrations were significantly associated with decreased odds of all hot flash outcomes. CONCLUSIONS: Although the temporality of such associations is not known because of the cross-sectional nature of the data, these observed relationships can help to identify women at risk for hot flashes.