The results of magnetic resonance imaging (MRI) studies performed on the knee region of 60 children including 20 normally growing subjects are reported. In healthy children, MRI permitted to study the normal maturation of bone marrow and cartilaginous structures. The patients studied had bone tumors (11 patients), rheumatoid arthritis (8 patients), lesions of traumatic origin (7 patients), osteochondritis (4 patients), vascular and tissular dysplasia (3 patients), osteomyelitis (3 patients) and soft-tissue tumors (3 patients). In all patients, MRI showed clinically relevant abnormalities that were not detected by conventional X-rays or physical examination. MRI offers the ability to study disorders of bone, bone marrow, cartilage, menisci and ligaments in a noninvasive way. MRI has replaced arthrography of the knee and is the examination of choice in pediatric patients.