OBJECTIVE: To determine the prevalence of virological failure and HIV drug resistance among Chinese patients one year after initiating lamivudine-based first-line antiretroviral treatment. METHODS: A prospective cohort study with follow-up at 12 months was conducted in four urban sentinel sites in China. Antiretroviral naive patients ≥18 years old were recruited. Blood samples were collected for testing CD4 cell count, viral load, and (for samples with HIV-1 RNA ≥1000 copies/ml) genotyping of drug resistance. RESULTS: A total of 513 patients were enrolled in this cohort, of whom 448 (87.3%) were retained at 12 months. The median final CD4 cell count was 313 cells/mm(3), which increased from 192 cells/mm(3) at baseline (P<0.0001). Of the 448 remaining subjects, 394 (87.9%) had successful... virological suppression (HIV RNA <1000 copies/ml). Among 54 samples with viral load ≥1000 copies/ml, 40 were successfully genotyped, and 11 were found with detectable HIV drug resistance mutations. Of these, the proportions of drug resistance to NNRTIs, NRTIs and PIs were 100%, 81.8% and 0%, respectively. Injecting drug use (AOR = 0.40, 95% CI: 0.19,0.84; P = 0.0154), CD4 count at baseline ≥350 cells/mm(3) (AOR = 0.32, 95% CI: 0.14,0.72; P = 0.0056), and missed doses in the past month (AOR = 0.30, 95% CI: 0.15,0.60; P = 0.0006) were significantly negatively associated with HIV RNA <1000 copies/ml. CONCLUSIONS: Our study demonstrates effective virological and immunological outcomes at 12 months among these who initiated first-line ART treatment. However, patients infected through drug injection, who missed doses, or with higher CD4 count at baseline are at increased risk for poor virological response.