We conducted a 2-year prospective cohort study to investigate multiple aspects of factors predicting the outcome of fixed-dose combination antiretroviral (ARV) therapy with lamivudine, stavudine, and nevirapine (GPOvir) at a government referral hospital in northern Thailand. At 6 and 24 months after the initiation of GPOvir, viral load (VL) was measured to determine virologic failure (>400 RNA copies/ml) and demographic, socio-economic, behavioral and clinical data were collected. From 10 April 2002 to 31 January 2004, 409 patients participated in this study: 64/364 (17.0%) at 6 months and 55/345 (15%) at 24 months virologically failed treatment. On univariate analysis, besides ARV experience [odds ratio (OR), 3.08, 95% confidence interval (CI), 1.71 -5.57] and the frequency of delayed doses (OR, 2.97; 95% CI, 1.47-6.00), we identified one socioeconomic factor significantly associated with virologic failure: "not having child" (OR, 1.85; 95% CI, 1.03 - 3.34). Although the association with "not having child" became marginal on multivariate analysis, results of in-depth interviews and group discussions indicated that having a child was a strong motivating factor for good treatment compliance. We suggest that patients without children may need more attention. Further investigation of socio-economic factors is warranted.