Background: Patients with primary hyperparathyroidism (PHPT) have continuously elevated parathyroid hormone (PTH) and consequently increased bone turnover with negative effects on especially cortical (Ct) bone with preservation of trabecular (Tb) bone. High resolution peripheral quantitative computed tomography (HR-pQCT) is a new technique for in vivo assessment of geometry, volumetric density and microarchitecture at the radius and tibia. In this study we evaluated bone status in women with PHPT compared with healthy controls using HR-pQCT. Subjects and Methods: A total of 27 patients with PHPT (median age 61, range 44-75 years) with median disease duration of 12 months (range 3-99 months) from diagnosis, and 27 age-matched healthy controls (median age 60, range 44-76 years) recruited by random sampling from the background population were studied using HR-pQCT (Scanco Medical) of the distal radius and tibia along with areal bone mineral density (aBMD) by dual energy x-ray absorptiometry (DXA) (Hologic) of the ultra-distal forearm, femoral neck and lumbar spine (L1-L4). Results: Groups were comparable regarding age, height and weight. In radius, patients had reduced Ct area (48.6 vs. 58.2 cm2, p=0.008) and Ct thickness (0.72 vs. 0.87 µm, p=0.01) along with reduced total (264 vs. 317 mg/cm3, p=0.002), Ct (844 vs. 892 mg/cm3, p=0.02) and Tb (101 vs. 125 mg/cm3, p=0.02) volumetric density as well as a reduced Tb number (1.41 vs. 1.71 mm-1, p=0.04) and increased Tb spacing (0.74 vs. 0.60 µm, p=0.05) compared with controls. In tibia, no differences in HR-pQCT parameters were found. Moreover, patients had lower ultra-distal forearm (0.307 vs. 0.345 g/cm2, p=0.005), spine (0.837 vs. 0.917 g/cm2, p=0.04) and femoral neck (0.645 vs. 0.705 g/cm2, p=0.03) aBMD compared with controls. Conclusion: A negative bone effect of continuously elevated PTH with alteration of HR-pQCT assessed geometry, volumetric density and both trabecular and cortical microarchitecture in radius but not tibia was found along with reduced aBMD by DXA in the forearm, spine and hip in female patients with PHPT.