The optimal timing for discontinuing treatment with a long-acting gonadotropin-releasing hormone (GnRH) analog (TAP-144SR) was investigated in patients with central precocious puberty (CPP). Thirty-five girls with CPP (21 with idiopathic disease and 14 with organic disease) were treated with the analog for 3 to 5 years. No significant differences were seen between the idiopathic and the organic CPP in the suppressive effect of bone maturation. Advancement of bone maturation was noticeably suppressed during the period between bone ages (BA) of 11.0 and 11.9. The height standard deviation score (Ht-SDS) for BA was consistently improved from 10 to 11.5 years of BA, and patients reached peak Ht-SDS at a BA of 11.5 years. The ΔHt-SDS (annual change in Ht-SDS) was noticeably decreased at BA over 12 years in spite of prolongation of the treatment. In the eight patients who have reached final height, the average Ht-SDS was -0.49 at end of the treatment (BA 11.7 years) and the final Ht-SDS was -1.1SD, respectively. Predicted adult height at the end of the treatment was significantly higher than the actual final height (P<0.01). The results suggest that a fall in Ht-SDS for BA which usually occurs at approximately 12 years of BA, is an indication for cessation of the treatment with TAP- 144SR, and residual growth potential judged solely from BA may be decreased in girls with CPP after discontinuation of the treatment.