OBJECTIVE: To estimate the prevalence of perceived poor sleep in women aged 35–49 years and to correlate sleep quality with levels of gonadal steroids and predictors of poor sleep. METHODS: A cohort of 218 black and 218 white women aged 35–47 years at enrollment (aged 37–49 at final follow-up) with regular menstrual cycles was identified through random digit dialing for a longitudinal study of ovarian aging correlates. Data obtained at four assessment periods, including enrollment, over a 2-year interval were collected between days 1 and 6 (mean = 3.9) of the menstrual cycle. The primary outcome measure was subjects’ rating of sleep quality at each assessment period. Associations of sleep quality with hormone levels (estradiol, follicle-stimulating hormone, luteinizing hormone, testosterone, and dehydroepiandrosterone sulfate) and other clinical, behavioral, and demographic variables were examined in bivariable and multivariable analyses. RESULTS: Approximately 17% of subjects reported poor sleep at each assessment period. Significant independent associations with poor sleep included greater incidence of hot flashes (odds ratio [OR] 1.52; 95% confidence interval [CI] 1.08, 2.12, P = .02), higher anxiety levels (OR 1.03; 95% CI 1.00, 1.06, P = .04), higher depression levels (OR 1.05; 95% CI 1.02, 1.07, P < .001), greater caffeine consumption (OR 1.25; 95% CI 1.04, 1.49, P = .02), and lower estradiol levels in women aged 45–49 (OR 0.53; 95% CI 0.34, 0.84, P = .006), after adjustment for current use of sleep medications. CONCLUSION: Both hormonal and behavioral factors were associated with sleep quality. Estradiol levels are an important factor in poor sleep reported by women in the 45–49 age group. Further evaluation of estrogen treatment for poor sleep of women 45 years and older is warranted.