We report clinical findings, bone mineral density (BMD) and bone biopsy data in ten children with features of classic idiopathic juvenile osteoporosis (IJO). We also screened the patients for mutations in LRP5 and LRP6. We found low BMD in the lumbar spine, the hip and distal radius. In the spine and distal radius, the reduction in BMD was more marked in the trabecular compartment. Biopsy confirmed that the trabecular compartment is more severely involved with reduction in bone formation and increase in bone resorption. No mutations in LRP5 and LRP6 could be identified. IJO is likely to be a heterogeneous bone disorder, and next-generation genomic sequencing studies may help reveal causative genes.