Osteochondromas are common tumors, but they rarely arise from the soft tissue adjacent to joints. Here we report on a patient who presented with a mass that had gradually grown over his right knee over 2 years. Preoperative studies included plain radiography and magnetic resonance imaging. Marginal excision was performed, and a fat-pad osteochondroma was diagnosed after pathological examination. Herein, we present the clinical, gross, histological and imaging features of this tumor. At 1-year follow-up, the patient’s outcome measures were good.