We report the case of five patients referred to our department with Hoffa's disease: three patients were at the initial stage of the disease and the two others had reached the chronic stage. This condition is one of the less well-documented causes of pain in the anterior compartment of the knee. The pathophysiological mechanism is still unclear. It is probably caused by repetitive micro trauma resulting in inflammatory, haemorrhagic and fibrous changes to Hoffa's fat pad. The final outcome of the disease is an osteochondroma. The diagnosis is established by MRI, which demonstrates inflammation of the fat pat. At the chronic stage, a standard X-ray is sufficient to demonstrate ossification of the fat pad.