One hundred and seventeen consecutive patients with 119 anterior cruciate deficient knees presenting to a knee clinic were studied to analyse an apparent poor diagnosis rate by referring doctors. The diagnosis had been made by the original treating physician in only 9.8 per cent of cases. Thirty per cent of the patients had been seen by an orthopaedic consultant without the diagnosis being made. Thirty-six patients had undergone 51 invasive investigations, including arthroscopy, without the diagnosis being made. This was despite 90 per cent of patients having a typical history and all having unequivocal physical signs. The average delay in diagnosis was 21 months.