Decreased height and weight in treated children with classical galactosemia have been reported. However, growth has not been extensively studied. Patients might be at risk for an abnormal growth because of either disease-related intrinsic factors or diet-related factors. The objective was to gain insight in growth in treated children and adolescents with classical galactosemia. The studied population was a previously reported group of 40 classical galactosemia children. Prenatal growth was evaluated using length, weight and head circumference (HC) data from welfare centers or parents. Postnatal growth was evaluated using three height and weight measurements at baseline, 1 and 2 years to calculate growth velocities. Height Z-score was also corrected for target height Z-score (height Z-score divided by target height Z-score). Linear regression analysis was performed between growth velocities, IGF-I, IGFBP-3, dietary intake and galactose-1-phosphate-uridyltransferase activity. We found normal length (median 50.5 cm), weight (median 3,255 grams) and HC (median 33.9 cm) at birth. Mean height growth velocity was 0.87+/-1.2 for boys and -0.89+/-2.1 for girls, and mean weight growth velocity was 0.91+/-1.6 for boys and -0.74+/-1.3 for girls. Mean height corrected for target height was -1.5+/-0.9 in girls and -0.6+/-0.7 in boys. Height growth velocity was correlated with IGF-I (Pearson correlation= 0.499), IGFBP-3 (Pearson correlation 0.4) and height Z-scores corrected for target height Z-scores (Pearson correlation=0.550). Five children grew beyond the age of 18 years. In conclusion, prenatal growth was normal but postnatal growth was affected. Predicted final height is less than target height in most patients; however, target height might be reached for the children who grow beyond the age of 18. Decreased IGF-I and IGFBP-3 and or suboptimal hormonal replacement in girls might play a role.