Intracortical osteosarcoma is a comparatively rare and distinct tumor separated from conventional osteosarcoma and other osteosarcoma variants. At first, the lesion was described in two patients by Jaffe in 1960. To date, 17 cases have been described in the literature. In all cases, the tumor occured in the cortex of the shaft of the femur or tibia. En-bloc resection was performed as primary therapeutic approach in most cases, sometimes in combination with neoadjuvant or adjuvant chemotherapy.

We, for the first time, describe a case of intracortical osteosarcoma of the midshaft of the right ulna which was found accidentaly in a patient taking part in a screening programm for heriditary breast cancer.

The patient underwent en-bloc resection without additional chemotherpapy and shows no reccurence after 18-months follow up.