Objective: To evaluate adult height (AH) in 25 girls with Turner syndrome (TS) who were treated from before 6 years of age for 10.0G1.7 years with a fixed GH dose of 0.33 mg/kg per week. Patients and design: After a 6-month pretreatment assessment all patients were measured 6-monthly under therapy to assess height SDS (H-SDS) and height velocity (HV) until AH achievement. Results: Following initial acceleration, HV declined after the first 4 years of therapy. At the end of the sixth year of therapy, H-SDS gain was 1.9G1.1. Thereafter, H-SDS gain from baseline decreased, becoming 0.9G0.9 SDS at AH achievement. Bone maturation velocity did not significantly change throughout the prepubertal period. According to Lyon standards for TS, mean AH SDS was significantly higher than pretreatment H-SDS (P!0.0001), with a mean H-SDS change of 0.9G0.9. However, the prevalence of patients with AH !K2 SDS (according to Sempé standards) was close to those recorded at the start of therapy (16/25 vs 18/25). No significant differences in terms of AH were found between patients with either X monosomy or X-chromosomal abnormalities and between girls with either spontaneous or induced puberty. Conclusions: We infer that the therapeutic regimen adopted in this prospective study is sufficient to induce a significant growth acceleration during the first year, but the response waned after 6 years of treatment.