Context Studies of all types of organ transplant recipients have suggested that weight gain, expressed as an increase in body mass index (BMI), after transplant is common. Objectives To describe weight gain during the first year after transplant and to determine risk factors associated with weight gain with particular attention to type of transplant. Design, Setting, and Participants A prospective study of 502 consecutive organ transplant recipients (261 kidney, 73 liver, 29 heart, 139 lung) to identify patterns of BMI change. Measurements were made during regular outpatient clinical visits at 2, 6, and 12 months after transplant. Data were retrieved from patients' charts and correlated with maintenance corticosteroid doses. Results Overall, mean BMI (SD; range) was 23.9 (4.5; 13.6–44.1) at 2 months and increased to 25.4 (4.0; 13.0–42.2) by the end of the first postoperative year. BMI levels organized by World Health Organization categories showed a trend toward overweight/obesity in kidney (53.4%), liver (51.5%), heart (51.7%), and lung (33.1%) patients by 12 months after transplant. BMI changed significantly ( P = .05) for all organ types and between all assessment points, except in kidney recipients. Maintenance corticosteroid doses were not a predictor of BMI at 12 months after transplant for most patients. Conclusions Weight gain was common among patients undergoing kidney, liver, heart, and lung transplant; however, many showed BMI values close to normality at the end of the first year after transplant. In most cases, increased BMI levels were related to obesity before transplant and not to maintenance corticosteroid therapy.