Serial measurements of elementary-school children were conducted for 2 consecutive years to assess height and growth velocity and to determine the prevalence of growth hormone deficiency (GHD) in American children. Trained volunteers measured 114,881 children the first year; 79,495 growth rates were calculated after the second measurements. The height and growth velocity curves generated were very similar to the currently used charts. We examined 555 children with short stature (< 3rd percentile) and poor growth rates (< 5 cm/yr). Five percent had an endocrine disorder. The presence of GHD (peak level, < 10 ng/dl with two provocative tests) was found in 16 previously unrecognized children; 17 children from this school population were already known to have GHD. Boys outnumbered girls 2.7:1 (p = 0.006). Six girls with Turner syndrome also were identified. We conclude that (1) the growth curves generated in the 1960s and 1970s are valid for children of the 1990s; (2) most children growing < 5 cm/yr (a commonly used threshold rate) will not have an endocrine disorder; (3) many children (48% in this study) with GHD and others with Turner syndrome may currently be unrecognized and untreated; (4) GHD appears to be more common in boys; and (5) the prevalence of GHD in the United States is at least 1:3480.