Among the causes of anterior knee pain, impingement of portions of the infrapatellar fat pad between the femoropatellar and femorotibial articular surfaces plays an important role. This disease, first described by Hoffa in 1904, has always been fairly obscure. This review of 63 cases delineates the clinical features, distinguishing two phases, acute and chronic, and analyzing the pathologic changes in the fat pad and the other joint structures involved. Treatment of both the chronic and acute phases is described, emphasizing the importance of arthroscopy in the chronic phase. The arthroscopic techniques are thoroughly described and commented on. Analysis of the results confirms the validity of arthroscopic surgery in the treatment of this disease.