The popularity of baseball has resulted in an increase in medical attention directed toward participating players. This study focuses on injuries of the throwing arm in adolescents which occur during participation in organized youth baseball matches. History taking, physical examination and roentgenographic study of both elbows were made on 67 adolescent baseball players who visited the Department of Orthopaedic Surgery of Hanyang Vniversity Hospital from December, 1981 to January, 1982. The results obtained were as follows: 1. The average age was 12.4 years and average career playing baseball was 1 year 11 months. 2. There were 18(85.7%) overhand type pitchers. This was the most common pitching style. 3. 7(10.4%) complained of elbow pain. In all cases the pain was located on the medial aspect of the elbow. 4, On physical examination, hypertrophy of the forearm was seen in 19(28.4%), hypertrophy of the arm in 27(40.3%), limb length discrepancy in 28(41.8%), cubitus valgus deformity in 2(3.0%), and flexion contracture of the elbow in 6(9.0%) cases. 5. On roentgenographic study, cortico-trabecular hypertrophy of the humerus, and separation and fragmentation of the medial humeral epicondyle were the common findings. 6. The pain and flexion contracture of the elbow were more marked in pitchers. 7. To prevent these injuries of the elbow, the following recommandations were made by authors. Use a pitching machine in batting exercise. Restrict the number of innings pitched per game, Abolish curve ball throwing in this age group. Ensue an adequate warmup period before exercise or games. Inform parents and coaches of the possible harmful nature of excessive throwing.