Recent European studies have shown that growth retardation is com-mon in people with phenylketonuria (PKU) during the first years of life while they receive a low-phenylalanine (Phe) diet. The aims of the present study were to assess the growth of our PKU patients and to search for nutritional and hormonal explanations for the growth delay. Twenty PKU patients aged 8 months to 7 years entered the study. The design was cross-sectional, a longitudinal study having already been performed in our centre. The following data were recorded: weight/height (W/H), height/age (H/A), and weight/age (W/A) Z-scores; fat-free mass (measured from bioelectrical impedometry (FFM1), and skinfold thickness (FFMA). Thyroid hormones, insulin-like growth factor I (IGF1), insulin-like growth factor binding protein (IGFBP3), selenium, zinc, and Phe blood levels were measured. Dietary intake was also recorded over 4 days. PKU patients were moderately but significantly shorter (H/A Z-score varied from -2.12 to 1.61; mean -0.49) and lighter (W/A Z-score varied from -2.58 to 1.49; mean -0.71) than the French reference population. Body composition was not different from that of controls matched for age and sex. IGF1, IGFBP3, and thyroid hormone levels were within normal range. All children received more than two-thirds of the recommended daily allowances for energy (91% +/- 18%) and for proteins (146% +/- 26%). The mean daily intake of our patients was sufficient in selenium, but markedly deficient in zinc (2.4 +/- 2.2 mg/day). No correlation was found between zinc daily intake or zinc plasma levels and growth retardation. Moreover, no relation was found between the plasma Phe concentrations, protein or caloric intake and the presence of growth retardation. Our results show that growth retardation in PKU patients is not related to hormonal or caloric deficiencies. Further studies are needed to investigate the effect of various nutrient supplementation regimens (especially zinc) on the growth of PKU patients.