Gestational weight gain (GWG) is important for health policy as it may be associated with overweight epidemics in childhood and adolescence. The purpose of the study was to perform the risk assessment of joint effects of the excessive GWG and the pregravid maternal BMI on overweight in infancy and childhood. The observations were collected in the ongoing prospective birth cohort study of 482 non-smoking mothers and their newborns in Cracow inner city area. At 5 years of age the subsample of 312 infants were reexamined in order to assess their nutritional status. Body fatness was assessed by means of the weight/length ratio (WLR) in neonates and weight/height ratio (WHR) in 5-year-olds since they showed the strongest correlation with subcutaneous fat mass of young children. In the statistical analysis the binary regression models were applied to identify predictors of overweight. The excessive GWG (>18 kg) increased more than twofold the adjusted relative risk (RR) of neonatal fatness (R=2.7; 95% CI 2.0-3.7) and was also a significant independent risk factor for postnatal body fatness at 5 years of age (RR=2.0; 95% CI: 1.3-3.3). The results confirmed earlier findings that pregravid overweight increased not only the relative risk of neonatal fatness (RR=2.9; 95% CI: 2.2-3.9) but also overweight in early childhood (RR=2.7; 95% CI: 1.7-4.4). The conclusion is that excessive GWG may be a risk factor for overweight in early childhood and should be a focus of public health policy.