BACKGROUND The appropriate timing of antiretroviral (ARV) therapy initiation in children with human immunodeficiency virus (HIV) infection has been uncertain. There was evidence of poorer outcome in adults who initiated treatment at lower baseline CD4 cell count. However, early initiation may not be possible in resource-limited setting and would increased risk of long term side effects and non-adherence. OBJECTIVE To elucidate the outcome of HIV-infected children who ARV treatment was initiated at different disease stages. METHODS Data from medical records of HIV-infected children who had been followed at Infectious Disease Division, Department of Pediatric Siriraj Hospital were retrospectively reviewed. Clinical response and outcome data were analyzed. RESULTS From September 1996 to March 2004, there were 200 patients with a median age at treatment initiation of 38 (2-175) months. The median duration of follow up period was 26 (1-91) months. The median baseline CD4 cell count was 545 (2-5016) cells/mm3. The median baseline CD4 percentage was 14.25 (0.11-60). Monotherapy or dual nucleoside reverse transcriptase inhibitor (NRTI) regimens were initiated in 134 (67%), and HAARTwas initiated in 66 (33%) patients. The survival rate in patients who initiated with HAART tended to be better than those initiated with dual NRTI regimens but salvaged appropriately (p=0.2377). The survival rate in those initiated treatment at baseline CD4 > or = 15% was better than those initiated at baseline CD4 < 15% (p=0.0471). CONCLUSIONS Initiation of ARV treatment at CD4 more than 15% resulted in a better survival rate than at CD4 below 15%. Initiation with HAART regimen tended to improve survival and resulted in higher CD4 gain especially in cases with baseline CD4< 15%.