The material from a case of Tietze's disease has been examined histologically. A review of the literature on the pathology of this lesion correlated with the findings from this case indicates that there is a pathological lesion in the costal cartilage in this disease. This consists of an increased vascularity and degenerative changes with patchy loss of ground substance leading to a fibrillar appearance. Cleft formation may occur with mucoid debris which may undergo calcification. Hypertrophic changes may be present at the periphery. The aetiology still remains obscure.