The infrapatellar fat pad of Hoffa is commonly injured but rarely discussed in the orthopaedic literature. Hoffa's disease is the extension of various traumatic events due to impingement and inflammation of the infrapatellar fat pad and known as a vague reason for anterior knee pain. Inflammation is foreground during acute phase of the disease while impingement due to fibrosis and scar tissue of infrapatellar fat pad plays a major role in the chronic phase. The osteochondroma of the infrapatellar fat pad secondary to the Hoffa's disease can be more problematic. Although, the fibrocartilaginous transformation and osteochondral metaplasia of infrapatellar fat pad was pointed out frequently in the literature, the published papers seem far from clarifying the relation between chronic impingement and formation of osteochondroma. We present a case of a giant ossifying chondroma in the infrapatellar fat pad that resulted from chronic Hoffa's disease. Complete open resection was performed successfully after arthroscopic examination. The infrapatellar fat pad contains the entire progenitor cells for the development of an osteochondroma and chronic impingement may have promoter affect on this issue, thus, an osteochondroma may occur at the end-stage Hoffa's disease.