Suboptimal final height and marked weight gain after renal transplantation (RTx) are common and may result in obesity. Steroid free immunosuppression has been advocated to improve growth and limit weight gain. We evaluated retrospectively the evolution of growth and body mass index (BMI) after renal transplantation to study risk factors for weight gain under steroid based treatment. Sixty-four pediatric patients (age 9.9 +/- 5.0 yr) were included in the study. To allow comparison between different age groups, standard deviation scores (SDS) for height and BMI for height age were calculated at time of transplantation and 3, 6, 9, 12, 24, 36, 48 and 60 months later. Induction immunosuppression consisted of basiliximab, cyclosporine and prednisone. Growth retardation at time of RTx was obvious with a SDS for height of -2.20 +/- 1.34. Height during the first year improved to an SDS of -2.0 +/- 1.27 (p < 0.01) but did further not increase in year 2 and 3. More than 40% of all patients remained 2 SDS below normal mean. SDS BMI for height age at transplantation was -0.19 +/- 0.98 and increased significantly during the first 3 months after transplantation to +0.64 +/- 1.07 (p < 0.01). Thereafter, BMI remained stable but did not decline to pretransplant values. A SDS BMI for height age of more than 2 SDS was observed in 2, 6, 9 and 11% of children at RTx and 1, 2 and 3 yr later respectively. BMI gain over 3 yr was significantly enhanced in children whose parents (especially the mother) were overweight. No influence of gender, BMI at RTx, dialysis modality prior to RTx or rejection episodes could be detected. We conclude that after RTx children exhibit some improvement in growth but height remains suboptimal. The BMI does increase significantly during the first months after RTx and does not return to baseline values under steroid-based immunosuppression. Obesity (>2 SDS above normal) does not occur more often than in the normal population. The most predictive parameter of inappropriate weight gain during 3 yr is the BMI of the mother. We would speculate that steroids may play a major role in weight gain in the early phase after RTx. However, genetic or environmental factors predict the long-term weight development.