The aim of this study was to correlate the distribution of substance-P nerve fibres within the knee joint in 20 patients complaining of anterior knee pain syndrome, with the clinical picture, patellar motion, power of the quadriceps mechanism, and the psychological profile. A comparison was made with 2 similar groups of patients with knee problems (patients with osteoarthrosis and patients with anterior cruciate ligament rupture or meniscal lesions), and with a further group of 20 healthy volunteers. The results suggest that anterior knee pain might be a psychosomatic syndrome associated with sub-clinical patellar instability and with little if any relation to levels of physical activity.