Background:The blood monocyte-to-lymphocyte ratio (MLR) is associated with active tuberculosis (TB) in adults, but has not been evaluated as a TB diagnostic biomarker in HIVinfected children in whom respiratory sampling is difficult. Setting:In a cohort of HIV-infected hospitalized Kenyan children initiating antiretroviral therapy, absolute monocyte and lymphocyte counts were determined at enrollment and 4, 12, and 24 weeks thereafter.Methods: Children were classified as confirmed, unconfirmed, or unlikely pulmonary TB. ROC curves of MLR cutoff values were generated to distinguish children with confirmed TB from those with unconfirmed and unlikely TB. General estimating equations were used to estimate change in MLR over time by TB status.Results: Of 160 children with median age 23 months, 13 (8.1%) had confirmed TB and 67 (41.9%) had unconfirmed TB. Median MLR among children with confirmed TB [0.407