Objective: To assess the effects of long-term growth hormone (GH) treatment for short stature on left ventricular (LV) dimensions and systemic blood pressure (BP) in girls with Turner’s syndrome without clinically relevant cardiac abnormalities. Study design: LV dimensions measured by echocardiography and systemic BP were assessed before and during 7 years of GH treatment in 68 girls with Turner’s syndrome participating in a randomized dose-response study. These previously untreated girls, age 2 to 11 years, were randomly assigned to 1 of 3 GH dosage groups: group A, 4 IU/m²/d; group B, first year 4 IU/m²/d, thereafter 6 IU/m²/d; group C, first year 4 IU/m²/d, second year 6 IU/m²/d, thereafter 8 IU/m²/d. After the first 4 years, girls ≥12 years of age began receiving 17β-estradiol, 5 μg/kg body weight per day, for induction of puberty. Results: At baseline the LV dimensions of almost every girl were within the normal range, and the mean SD scores were close to zero. During 7 years of GH treatment, the growth of the left ventricle was comparable to that of healthy girls. No signs of LV hypertrophy were found. Before the start of GH treatment, mean BP was within the normal range but significantly higher than in healthy control subjects. Diastolic BP and systolic BP were above the 90th percentile in 23% and 28% of the girls, respectively. After 7 years of treatment, these percentages were 14% and 36%, respectively (not significantly different from baseline). The SD score of the diastolic BP showed a small decrease after 7 years of treatment. The growth of the left ventricle and the development of BP were not different between the GH dosage groups. Conclusions: Long-term GH treatment, even at dosages up to 8 IU/m²/d, does not result in LV hypertrophy or hypertension in girls with Turner’s syndrome. Continued observation into adulthood is recommended to monitor the further development of the relatively high BP and to ensure that GH treatment has no long-term negative effect on the heart. (J Pediatr 1999;135:470-76)