The authors describe two cases of pulmonary fibrosis in patients suffering from ankylosing spondylitis. The diagnosis of tuberculosis was rejected on the basis of negative studies for tubercle bacilli and the total ineffectiveness of specific therapy. No evidence of microbial or parasitic infection was found. This fibrosis was associated with a considerable worsening in general condition. Nevertheless, the first patient remains alive 15 years after the onset of this pathological manifestation. The second patient died but autopsy was not possible. A wide review of the literature is undertaken in the light of these two cases.