Osteogenesis imperfecta (OI) is a hereditary disorder characterized by decreased biosynthesis or impaired morphology of type I collagen that leads to decreased bone mass and increased bone fragility. We hypothesized that patients with OI have altered bone microstructure and bone geometry. In this cross‐sectional study we compared patients with type I OI to age‐ and gender‐matched healthy controls. A total of 39 (13 men and 26 women) patients with OI, aged 53 (range, 21–77) years, and 39 controls, aged 53 (range, 21–77) years, were included in the study. Twenty‐seven of the patients had been treated with bisphosphonates. High‐resolution peripheral quantitative computed tomography (HR‐pQCT) at the distal radius and distal tibia and dual‐energy X‐ray absorptiometry of total hip, femoral neck, trochanteric region, and the lumbar spine (L1–L4) were performed. The patients were shorter than the controls (159 ± 10 cm versus 170 ± 9 cm, p < 0.001), but had similar body weight. In OI, areal bone mineral density (aBMD) was 8% lower at the hip (p < 0.05) and 13% lower at the spine (p < 0.001) compared with controls. The trabecular volumetric bone mineral density (vBMD) was 28% lower in radius (p < 0.001) and 38% lower in tibia (p < 0.001) in OI compared with controls. At radius, total bone area was 5% lower in OI than in controls (p < 0.05). In the tibia, cortical bone area was 18% lower in OI (p < 0.001). In both radius and tibia the number of trabeculae was lower in patients compared to the controls (35% and 38%, respectively, p < 0.001 at both sites). Furthermore, trabecular spacing was 55% higher in OI in both tibia and radius (p < 0.001 at both sites) when compared with controls. We conclude that patients with type I OI have lower aBMD, vBMD, bone area, and trabecular number when compared with healthy age‐ and gender‐matched controls. © 2012 American Society for Bone and Mineral Research.