Chest wall protrusion and depression deformities, also known as funnel chest and pigeon chest, are nosologically a uniform entity. Our own histopathological studies revealed secondary changes, found likewise in arthroses, scolioses, aseptic osteonecroses and inflammatory processes, as well as changes found in so-called primary collagenous diseases of unknown aetiology. Investigation of the collagen metabolism did not disclose differences from the normal II-type collagen either qualitatively or quantitatively. The aetiology of funnel chest and pigeon chest can be defined as follows: A hereditary disturbance of metabolism results in weakening of the wall of the parasternal cartilage, effecting a deformation secondary to mechanical strain by respiration and growth. Psychocosmetic reasons are recognised as indication for operation. In our opinion, the optimal age for operation is the second to the sixth year of life. During 20 years, 765 patients were operated on at our hospital without lethality. Postoperative complications were pneumothorax (4%), pneumonia (2%), after bleeding (2%) and disturbed wound healing (7%). Late results 5 years following surgery were excellent in 57%, good in 27%, satisfactory in 10% and unsatisfactory in 6% of the cases, thus adding up to 84% good results.