Hoffa's disease, an obscure cause of anterior knee pain resulting from impingement and inflammation of the infrapatellar fat pad, was first reported by Albert Hoffa in 1904. Since the initial description, the clinical and pathological processes with an acute-to-chronic progression have been defined. Despite reports of eventual fibrocartilaginous transformation and ossification of the fat pad, no relation has been described between chronic impingement and the development of ossifying chondroma. We present a case of a unilateral, ossifying chondroma in the infrapatellar fat pad that resulted from chronic impingement and repetitive microtrauma. This case shows the radiologic, histologic, and pathologic features of Hoffa's disease. Successful arthroscopic resection is presented. A possible relationship between impingement of the infrapatellar fat pad and the development of ossifying chondroma may exist.