© 2016 by De Gruyter. Background: Low vitamin D level is associated with adverse health outcomes and compromises HIV treatment response. We assess vitamin D status in HIV-infected Thai children receiving combination antiretroviral therapy (cART). Methods: A cross-sectional study in perinatally HIV-infected children. Vitamin D deficiency and vitamin D insufficiency were defined as serum 25-hydroxyvitamin D (25-OHD) level < 20, and 21-29 ng/mL, respectively. Results: Eighty participants were enrolled. Their median age was 12.2 years. The median CD4 lymphocyte count was 784 cell/mm3; 95% had HIV RNA < 50 copies/mL. The median (interquartile range, IQR) 25-OHD level was 33.5 (26.2-39.8) ng/mL. Thirty-four (43%) participants had low vitamin D level; 26 (33%) and 8 (10%) had vitamin D insufficiency and deficiency, respectively. In multivariate analysis, only geographic location was significantly associated with low vitamin D level. Conclusions: Most of perinatally HIV-infected children receiving cART had low vitamin D level. Calcium and vitamin D supplement might be beneficial.