PURPOSE: The progressivity of central precocious puberty (CPP) seems to depend on the age at presentation. We evaluated the clinical courses of CPP girls according to their age at initiation of treatment. METHODS: One hundred thirty five girls with CPP diagnosed between Jan. 2003 and Dec. 2009 and regularly followed for more than one year were included. They were treated with gonadotropin-releasing hormone agonists (GnRHa) every four weeks. Subjects were divided into two groups based on whether they were treated before (Group I, N=20) or after seven years of age (Group II, N=115). We compared the anthropometric parameters, the predicted adult height (PAH), predicted treatment periods, and the laboratory findings of the two groups every six months. RESULTS: Out of 135 CPP patients, 123 were idiopathic and twelve had neurogenic problems. At the baseline, patients' average bone age (BA) was significantly older than chronologic age (CA) and PAH was significantly shorter than target height (TH). BA and CA were significantly older in group II, but the BA/CA ratio was significantly greater in group I. The average treatment period required to overcome the CA-BA difference was 4.64 yr (group I vs II; 7.98 yr vs 4.24 yr, P < 0.01), and the period needed to overcome PAH-TH difference was 2.49 yr (group I vs II; 4.37 yr vs 2.32 yr, P < 0.01). CONCLUSION: Among the girls with CPP, the younger age group had more advanced BA than CA, and needed significantly longer treatment periods to overcome the BA-CA gap and PAH-TH gaps.