To present longitudinal data on the psychological profile of a cohort of girls with and without Turner syndrome (TS) treated for 3 years with growth hormone (GH). Among a sample of 283 children with short stature, 37 girls with TS were recruited at 27 US medical centers. Of the original cohort, 22 girls with TS, 13 girls with isolated growth hormone deficiency (GHD), and 12 girls with idiopathic short stature were followed through 3 years of GH therapy. All were school-age, were below the 3rd percentile for height, had low growth rates, and were naive to GH therapy. Psychological tests (the Wide Range Achievement Test and the Slosson Intelligence Test) were administered to the clinical groups within 24 hours of their first GH injection and yearly thereafter. Control subjects were 25 girls with normal stature matched for age and socioeconomic status, who were tested only at baseline. One parent of each subject also completed the Child Behavior Checklist for that subject. At baseline, the clinical groups had more internalizing behavioral problems, had fewer friends, and participated in fewer activities than did the control subjects. The groups did not differ in mean IQ or academic achievement, but the TS group did have more problems in mathematics achievement. Height and growth rate significantly increased in the clinical groups over the 3 years of GH therapy, but IQ and achievement scores did not. Significant linear reductions were noted in both Internalizing and Externalizing Behavior Problems after GH treatment, with the TS group having fewer behavior problems before and after GH treatment than did the GHD-idiopathic short stature group. Decreases in specific Child Behavior Checklist subscales, including attention, social problems, and withdrawal, also were seen in the clinical groups after GH therapy. The comprehensive treatment of girls with TS should include educational and behavioral interventions in addition to traditional medical therapies.