Osteoporosis is the commonest skeletal disorder affecting millions of people and costing billions of dollars annually. Bone mineral density is highly heritable, but only 5.8% of the phenotype variance is currently accounted for. Current treatments reduce fracture risk by only 50% and there is urgent need to define new pathways that regulate bone turnover and strength. We hypothesised that rapid-throughput skeletal phenotyping of mice generated by the International Knockout Mouse Consortium would identify novel susceptibility alleles for bone and mineral disorders and provide in vivo models to elucidate their molecular basis. Adult translocation associated membrane protein-2 knockout mice (Tram2^-/-) had reduced body weight and deafness, and suffered spontaneous fractures despite normal serum biochemistry. Detailed analysis (X-ray microradiography, micro-CT, backscattered-electron scanning-electron microscopy, biomechanical testing, n=6 per gender, per genotype) by the Origins of Bone and Cartilage Consortium (http://www.boneandcartilage.com) demonstrated short stature (P<0.001, ANOVA), grossly reduced bone mineral content and mineralisation (P<0.001, Kolmogorov-Smirnov test), profoundly reduced cortical (P<0.001, ANOVA) and trabecular bone mass (P<0.001, ANOVA), and decreased bone strength and stiffness (P<0.001, ANOVA) in Tram2^-/- mice. Male homozygotes were more severely affected than females, whilst heterozygotes of both genders were unaffected. Tram2 lies downstream of BMP/Runx2 in osteoblasts and has been associated with fracture in genome-wide association studies. Tram2 is thought to be a component of the translocon, a multi-molecular channel that controls posttranslational processing of secretory proteins and may facilitate folding of type 1 collagen. However, we found no abnormalities of type 1 collagen structure by electron microscopy and no differences in expression of the unfolded protein response genes sXbp1, tXbp1, usXbp1, Ddit3, Edem1 and Hspa5 in Tram2^-/-mice. These data highlight Tram2 as a major regulator of bone mineralisation, structure and strength. Elucidation of its mechanism of action will identify new therapeutic targets for prevention and treatment of osteoporosis.