Knee problems in children are encountered regularly by primary care physicians. It is important to carry out a thorough clinical examination. Referred pain from a back or hip disease should be excluded during the examination. The need for further investigations depends on the degree of clinical signs present. Most knee problems in growing children - often vaguely associated with exercise or physical activity - are so mild that they do not cause functional impairment. However, a significant mechanical defect, an overuse injury or arthritis may be suspected if the pain makes the patient limp continuously or limits sports activities, or if the patient describes mechanical locking of the knee or, for example, dislocation of the patella. The affected knee should be compared with the contralateral knee. Positive clinical signs include the following: limited range of motion, instability, effusion, synovial swelling, other swelling or deformity, differences in temperature (heat or coolness), atrophy of thigh muscles, local tenderness in sites typical of overuse injuries, asymmetrical tenderness during patellofemoral compression, continuous limping and a side-to-side difference when squatting on one leg.