**OBJECTIVES: **People who are close to retirement age show the highest rates of weight gain and obesity. We investigate the effect of retirement on the change in body mass index (BMI) in diverse groups varying by wealth status and occupation type.

**METHODS: **Six panels of the Health and Retirement Study (1992-2002) on individuals aged 50-71 were used (N = 37,807). We used fixed-effects regression models with instrumental variables method to estimate the causal effect of retirement on change in the BMI.

**RESULTS: **Retirement leads to modest weight gain, 0.24 BMI on average. Weight gain with retirement was found among people who were already overweight and those with lower wealth retiring from physically demanding occupations. The cumulative effect of aging among people in their 50s, however, outweighs the effect of retirement; the average BMI gain between ages 50 and 60 is 1.30, 5 times the effect of retirement.

**CONCLUSIONS: **Given the increasing number of people approaching retirement age, the population level impact of the weight gain ascribed to retirement on health outcomes and health care system might be significant. Future research should evaluate programs targeted to older adults who are most likely to gain weight with retirement.