The vast majority of knee problems can be diagnosed by taking a complete history, performing a comprehensive physical examination, and obtaining appropriate x-ray films. However, diagnosis of anterior and posterior cruciate ligament tears, patellofemoral subluxation, tibial tubercle fracture, and fibular head dislocation is challenging because they often present like common, less serious knee disorders. Accurate assessment of these five injuries depends upon the examiner's knowledge of the specific presenting complaints and the subtle clinical and radiologic findings associated with these conditions.