Introduction: Pediatric forearm fracture is one of the most common upper extremity fractures in young sters. The treatment is often non-surgical. In patients, who need surgical intervention, intramedullary nails are used. Growth disturbances in long bones of the lower extremity occur in youngsters however. Longitudinal overgrowth is very rare in the upper extremity. Case Presentation: This report presents a five-year-old child, who had radius and ulna shaft fracture in the distal one third of his forearm. This child was treated with radius fracture fixation by flexible intramedullary nails. After six months, the child had wrist pain and limitation in range of motion. On the radiography, 4 mm increase in radius was observed. Conclusions: Overgrowth of long bones after application of intramedullary nails is known in the lower extremity however it is uncommon in the upper extremity and the exact mechanism of this phenomenon has not yet been determined and needs further investigation.