Acute periarticular knee injuries in athletes are common in sports requiring frequent cutting, deceleration, pivoting and jumping, and may substantially affect both short- and long-term athletic performance. Injuries of the anterior and posterior cruciate ligaments, meniscal tears, collateral ligament sprains, patellofemoral instabilities and extensor mechanism disruptions constitute the major pathology group leading to functional loss and recurrent instability. In addition, patellar, quadriceps, pes anserinus and popliteus tendinopathies; traction apophysitis such as Osgood-Schlatter and Sinding- Larsen-Johansson disease; and osteochondritis dissecans are significant causes of pain and performance limitation, particularly in young and active athletes. Accurate diagnosis requires a combination of detailed history, targeted physical examination maneuvers and appropriate imaging modalities. This review focuses on the diagnostic and differential diagnostic principles of acute knee injuries in athletes, whereas treatment approaches are addressed in the related sections.