To check the possible existence of long-term pulmonary functional sequelae in patients with pneumonia due to Mycoplasma pneumoniae, 17 patients who showed evident spirometric disorders during the recovery from the acute phase of a pneumonia due to Mycoplasma pneumoniae were studied. In the acute phase of the disease, 7 patients showed a ventilatory restriction, 6 of them had an obstructive pattern while in four patients a mixed pattern was observed. After a latency period, which mean length was 39 months, it was seen that there was a return to normal values of the spirometric conventional parameters initially altered in all cases. However 5 patients (33%) who did not smoke, showed a significant decrease on the maximum flows at low volume. These results suggest that in a high percentage of adult patients, as has been previously described in children, pneumonia due to M. pneumoniae could leave as a sequelae the persistent affectation of small airway.