ObjectiveTo evaluate bone mineral mass in adolescents with failure to thrive in relation to body composition.MethodsA case control study involving 126 adolescents (15 to 19 years), in final puberty maturation being 76 eutrophic and 50 with failure to thrive (genetic or constitutional delay of growth), of matching ages, gender and pubertal maturation. The weight, height and calculated Z score for height/age and body mass index; bone mineral content, bone mineral density and adjusted bone mineral density were established for total body, lower back and femur; total fat-free mass and height-adjusted fat-free mass index, total fat mass and height-adjusted. The statistical analyses were performed using the Student's t-test (weight, height and body composition); Mann-Whitney test (bone mass) and multiple linear regression (bone mass determinants).Resultsweight, height and height/age Z-score were significantly higher among eutrophic subjects. Both groups did not show statistically significant differences for fat mass, percentage of fat mass, total fat mass height adjusted and fat-free mass index height sadjusted. However, total free fat maass was smaller for the failure to thrive group.ConclusionsThere was no statistically significant difference for bone mass measurements among adolescents with failure to thrive; however, the factors that determine bone mass formation should be better studied due to the positive correlation with free fat mass detected in these individuals.