Aim: To investigate the association of calcium (Ca) and vitamin D (vit D) supplementation with bone mineral density (BMD) in pediatric acute lymphoblastic leukemia (ALL). Materials and Methods: Group I (n=11): de novo ALL patients aged 1 to 18 years. Group II (n=46): pediatric ALL survivors in first complete remission and ALL patients on maintenance chemotherapy. We stratified group II into 3 subgroups according to the postdiagnosis period (group IIa: 8 to 24 mo, group IIb: 24 to 48 mo, group IIc: >48mo). Group III (n=22): healthy siblings of group II. Daily oral vit D3 and Ca carbonate was given only to group I. In group I, BMD was measured at diagnosis and after completion of intensive chemotherapy (TP1 and TP2). Results: A significant increase in Ca (P=0.024) and 25-OH vit D (P=0.01), and a decrease in magnesium (P=0.023) were detected at TP2 compared with TP1 in group I. Mean plasma levels of 25-OH vit D were <20ng/mL in all the groups. Total body (P=0.005), total body less head (P=0.005), and L1 to L4 BMD Z scores (P=0.025) decreased significantly at TP2 compared with TP1. The lowest BMD scores were found at 8 to 24 months after diagnosis in unsupplemented patients. A gradual increase in BMD Z scores was shown, with the highest scores in group IIc. Conclusion: Vit D and Ca supplementation in pediatric ALL patients during intensive chemotherapy may not prevent bone mineral loss. BMD scores of pediatric ALL patients described by other studies, as a major decrease in the first 2 years and gradual increase afterward, was also observed in our patients.