Skeletal deformation like genu valgum is reported to be rare in Primary hyperparathyroidism (PHPT). The solitary adenoma or hyperplasia of the parathyroid glands are the cause in 80-85% of the cases. We report 2 cases of girls on 12 years and 15 years of age, complaining from pain and genu valgum deformation of the lower extremities before the planned orthopaedic surgical correction. The first patient had complaints for 3 years and lost ability to walk independently, the second case lost normal gate for a period of 5 months. The paraclinical screening discovered hypercalcemia, hypophosphatemia, elevated alkaline phosphatase, normal creatinine, raised parathormone. In the first case the X-rays depicted fibrocystic osteodistrophy from a hyperparathyroid type with bone cysts, giant cell "brown tumors" and pathological bone reorganization, in the second case - coarse fibrous structure of the left knee joint with genu valgum with bone cysts in the distal metaphysis of the left femur. The ultrasound of the thyroid gland found oval hypoechoic formations with suspicious origin from the parathyroid glands. These findings were confirmed from the SPECT/CT pointing active adenomas in the parathyroid glands. Skeletal deformation like genu valgum is the reason to search for the primary diagnosis in our 2 cases. Investigation of the serum calcium and parathormone are diagnostic in 100%. The imaging diagnosis has a critical role for indicating surgical treatment of the parathyroid gland adenoma. Key words: genu valgum, hypercalcemia, paediatric parathyroid adenoma, ultrasound, SPECT/CT.