We reviewed the arthroscopic findings in 16 knees in which a patellectomy had been performed 1-47 years previously (average 15.4 years). The study group consisted of 13 women and 3 men with an average age of 46.3 years (range 22-64 years). The knee symptoms had failed to respond to non-operative treatment and the treating surgeon (R.J.B.) had determined that arthroscopic examination was warranted. Fifteen of the 16 patients had articular cartilage damage, particularly in the medial compartment and trochlear groove. The severity of articular cartilage damage correlated with time since patellectomy, but not with patient age. Apart from the previous patellectomy, no predisposing factors could be identified to account for the frequency and severity of tibiofemoral osteoarthritis in this relatively young group of patients. Our findings suggest that there may be an association between patellectomy and the subsequent development of osteoarthritis.