Background: Little is known about spontaneous growth of growth hormone (GH)-deficient children during infancy and childhood. Methods: Retrospectively, we calculated disease-specific pretreatment percentiles for height, weight, BMI and growth velocity of 113 GH-deficient boys and 41 GH-deficient girls from birth until 7 years of age, by mean and standard deviation. Results: Infants with idiopathic GH deficiency (GHD) grow in disease-specific percentile channels. There is a significant difference in length and weight from birth onward compared to regional reference (p < 0.001). Boys’ birth length was 48.7 ± 2.9 cm (p < 0.001; –1.31 ± 1.11 SDS), birth weight was 3.09 ± 0.61 kg (p < 0.01; –0.92 ± 1.19 SDS), and BMI at birth was 12.9 ± 1.7. Girls’ birth length was 48.1 ± 3.4 cm (p < 0.05; –1.17 ± 1.51 SDS), birth weight was 2.92 ± 0.60 kg (p = 0.05; –1.08 ± 1.19 SDS), and BMI at birth was 12.6 ± 2.2. There was a continuous loss of growth velocity, despite a wide variance in the first years, so height deficit became more evident with increasing age. Conclusion: GHD is a congenital disease no matter when height deficit becomes clinically evident, because GH-deficient children grow in disease-specific percentile channels with a highly significantly reduced length and weight, which demonstrates that GH is essential for adequate growth in infancy and early childhood.