© Copyright The Authors 2016. Objective To examine whether weight history and weight transitions over adult lifespan contribute to physical impairment among postmenopausal women. Design BMI categories were calculated among postmenopausal women who reported their weight and height at age 18 years. Multiple-variable logistic regression was used to determine the association between BMI at age 18 years and BMI transitions over adulthood on severe physical impairment (SPI), defined as scoring <60 on the Physical Functioning subscale of the Rand thirty-six-item Short-Form Health Survey. Setting Participants were part of the Women's Health Initiative Observational Study (WHI OS), where participants' health was followed over time via questionnaires and clinical assessments. Subjects Postmenopausal women (n 76 016; mean age 63·5 (sd 7·3) years). Results Women with overweight (BMI=25·0-29·9 kg/m2) or obesity (BMI≥30·0 kg/m2) at 18 years had greater odds (OR (95 % CI)) of SPI (1·51 (1·35, 1·69) and 2·14 (1·72, 2·65), respectively) than normal-weight (BMI=18·5-24·9 kg/m2) counterparts. Transitions from normal weight to overweight/obese or to underweight (BMI<18·5 kg/m2) were associated with greater odds of SPI (1·97 (1·84, 2·11) and 1·35 (1·06, 1·71), respectively) compared with weight stability. Shifting from underweight to overweight/obese also had increased odds of SPI (1·52 (1·11, 2·09)). Overweight/obese to normal BMI transitions resulted in a reduced SPI odds (0·52 (0·39, 0·71)). Conclusions Higher weight history and transitions into higher weight classes were associated with higher likelihood of SPI, while transitioning into lower weight classes for those with overweight/obesity was protective among postmenopausal women.