A prospective study was conducted during one year to evaluate injuries in Brazilian Junior tennis players during the national circuit, in 2001. Male and female athletes in the age categories under 12, under 14, under 16 and under 18 years, all members of The Brazilian Tennis Confederation, participated in the study. Two physiotherapists and/or one physician evaluated the athletes. A total of 280 medical examinations were performed in 151 tennis players who needed medical treatment during the tournaments. The 151 athletes had 1-6 medical treatments during the tournaments and the mean was 1.8 treatment per athlete. The overall incidence was 6.9 medical treatments for every 1,000 games played. Medical assistance tothe athletes was performed on court in 83 (29.6%) occasions, 185 (66.1%) at the medical department and in both in 12 (4.3%) occasions. Retirement of the match was reported in 9 (3.2%) lesions. The most frequent injuries were: muscle contractures (76 - 27.14%), muscle pain/fatigue (36-12.85%), muscle strain (35-12.52%), tendinopathies (20 - 7.14%), cramps (16 -5.71%), ankle sprain (12 -4.28%) and low back pain (10-3.57%). Muscle pathology was the major source of injuries causing the athlete to seek medical assistance. Preventative measures are important to reduce the number of injuries, which may include muscle stretching programs and adequate nutrition and hydration.