This study sought to investigate associations between levels of high-sensitivity c-reactive protein (hsCRP) prior to treatment and change in depressive symptoms and cognition in a short-term, double-blind, placebo-controlled study of lurasidone in children and adolescents with bipolar I depression. Patients 10-17 years of age with a DSM-5 diagnosis of bipolar I depression were randomized to 6 weeks of double-blind treatment with flexibly dosed lurasidone (20-80 mg/day) (n = 173) or placebo (n = 170). The primary efficacy measure was change from baseline to week 6 in the Children’s Depression Rating Scale, Revised (CDRS-R). Treatment response was defined as 50% or greater improvement on the CDRS-R from baseline to week 6. Cognitive function was evaluated with the computerized Brief Cogstate Battery at baseline and week 6. Analyses were adjusted for baseline BMI, as well as age. HsCRP was evaluated as a logarithmically transformed continuous variable and as a categorical variable dichotomized into lower (<1 mg/L) and higher (≥1 mg/L) subgroups. A significant interaction was found between baseline hsCRP and treatment group for change in CDRS-R score at study endpoint, with larger placebo-corrected effect sizes for lurasidone in the higher baseline hsCRP group (≥1 mg/L). A significant BMI-by-hsCRP-by-treatment interaction was found for response rate with higher baseline hsCRP levels associated with greater antidepressant response to lurasidone (vs. placebo) in the normal BMI range subgroup (NNT = 2 in higher hsCRP vs. NNT = 5 in lower hsCRP groups) but not in the overweight/obese patients (NNT = 6 in higher hsCRP vs. NNT = 5 in lower hsCRP). Similarly, a significant interaction effect was observed for the combination of hsCRP and BMI on the procognitive effect of lurasidone, with higher baseline hsCRP levels being associated with improvement in cognitive function for lurasidone (vs placebo) in the normal BMI range subgroup but not in overweight/obese patients. These results suggest that young patients with bipolar depression with normal weight and higher levels of pre-treatment CRP may show a greater placebo-adjusted improvement in depressive symptoms and cognitive performance when treated with lurasidone. If these findings are confirmed in future prospective studies, CRP and BMI may prove to be useful diagnostic and predictive biomarkers in the treatment with lurasidone of children and adolescents with bipolar depression.