The efficacy of long-term growth hormone treatment and the optimal treatment modalities in Turner's syndrome are still controversial. Studies have shown widely divergent results. While there is still need for results of randomized controlled trials, large uncontrolled trials remain a valuable source of preliminary information. This study of 136 girls with Turner's syndrome (TS) from the European Lilly Turner Study shows that the treatment regimens followed by girls with TS who start GH treatment at a relatively late age (12.9 +/- 2.2 yr) lead at best to a small average gain in final height. Mean gain over initial projected final height was 3.7-4.7 cm, depending on the chosen Turner-specific height-for-age reference data. There was a considerable variation in gains over initial projected final height (range -10.6 to +17.2 cm), which may be partly explained by the existence of good and bad responders. Whether there is a genetic/molecular basis for this and how responsiveness can best be predicted remains an important challenge.