Adjusted odds ratios of early menopause by BMI in 1989, multivariable odds ratios and 95% confidence intervals (CIs) of early natural menopause were derived from restricted cubic spline models. Data from Nurses Heatlth Study II 1989–2011, adjusted for age at baseline (continuous), race/ethnicity (non-Hispanic White, Asian, Other), physical activity (<3, 3–49, >49 metabolic equivalent task (MET)*h/week), pack-years cigarette smoking (0, 1–10, 10–15, >15 pack-years), alcohol consumption (0, 0–10, 10–30, ≥30 g of alcohol). The reference BMI is 20.5; a total of 21 knots were specified ranging from BMI of 17.7 to 37.5 with likelihood ratio tests comparing models with and without cubic spline terms to assess non-linearity yielding P < 0.0001.