Case histories and previous chest X-ray films of 142 patients with bacteriologically confirmed active pulmonary tuberculosis from eastern Finland were re-examined. In 18% of the series the disease was a reactivation of previously diagnosed and treated tuberculosis. In 70% of the patients with first clinical attack of tuberculosis, previous RP-films revealed fibrotic lesions in the lungs. Only 23% of the whole series had no previous abnormality on chest X-ray examination or previous clinical tuberculosis. Fibrotic pulmonary lesions are therefore a significant risk factor in the epidemiology of pulmonary tuberculosis, which has been given too little attention.