FIAT (Factor Inhibiting ATF4-mediated Transcription) interacts with ATF4 to repress its transcriptional activity. We performed a phenotypic analysis of Fiat-deficient male mice (Fiat-/Y) at 8 and 16 weeks of age. Fiat-/Y mice appeared normal at birth and weight gain was comparable between genotypes. μCT analysis of proximal femur demonstrated 46% and 13% age-dependent increases in trabecular bone volume and thickness, respectively, in Fiat-/Y mice.