This retrospective review of clinical records and chest radiographs (CR) of adolescents aged 10-18 years was designed to determine age and sex differences in the clinical and radiological features of adolescent tuberculosis (TB). Records of adolescents who were admitted to Brooklyn Hospital for Chest Diseases (BCH) or who were treated at local authority health clinics were screened. Data from 324 adolescents (male:female ratio 1:1.2) were studied. Intra-thoracic lesions were present on CR in 306 (94%). Primary TB with mediastinal adenopathy was present in 32 (10%). Cavitation was present in 180 (56%), 16% at 10 and 73% at 18 years of age. Cavitation occurred in 55% of males and in 56% of females with increasing frequency from 15 years of age in the former and from age 14 in the latter. Microbiological confirmation of diagnosis was obtained in 254 (78%) cases, 52% in those aged 10-13 years and 86% in those > or = 14 years. Pleural effusion was present in 42 (13%), 26 males and 16 females (p < 0.05). Thirteen (7%) of the 182 hospitalized adolescents and 27 (19%) of the ambulant group did not complete therapy. The nature of tuberculous disease in adolescents changed dramatically with increasing age.