Objective: In repair of thoracic wall deformities, there is a debate in the literature regarding the optimal age and the type and number of costal cartilage resections. We evaluated the effect of costal cartilage resections on the chest wall development in young rabbits. Methods: Fifty apparently healthy, 6 weeks of age, male New Zealand white rabbits were evaluated in five groups, each including 10 subjects. Group 1 served as control for the observation of normal thoracic development. Rabbits in group 2 underwent partial and rabbits in group 3 underwent total resections of the right third and fourth costal cartilages; those in group 4 underwent partial and rabbits in group 5 underwent total resections of the right third to sixth costal cartilages. Anteroposterior, horizontal and vertical diameters of the chest were measured before operation and repeated at 24 weeks of age. Results: Upper and lower anteroposterior diameters of the thoracic wall and horizontal diameters of the left hemithorax differed significantly among groups (p = 0.011, p = 0.004, and p = 0.002, respectively). Upper anteroposterior diameter was 49 mm in group 1 and 44 mm in group 3 (p = 0.009). Lower anteroposterior diameter in group 5 (66 mm) was significantly less than that in group 1 (70 mm) (p = 0.039) and there was also a statistically significant difference between group 4 (71 mm) and group 5 (66 mm) (p = 0.002). Horizontal diameters of the left hemithorax in group 3 (32 mm; p = 0.005) and 5 (32 mm; p = 0.008) were significantly different when compared to group 1 (26 mm). Growth in right hemithorax was statistically less than that in left side in all operated groups except in group 2. Conclusions: Thoracic resections in young rabbits have demonstrated that the costal cartilage resection is not an innocent procedure as it severely affects the chest wall development especially in anteroposterior direction and the thoracic growth is markedly retarded when growth centers of the ribs are not preserved and/or four or more ribs are resected. © 2007 European Association for Cardio-Thoracic Surgery.