After an average follow-up of 6.5 yr (range 1 to 13), 48 of 48 patients with cedar asthma, who were still working in the same industry, were re-examined. In all of them, the diagnosis of cedar asthma had been confirmed with a specific challenge inhalation test with plicatic acid. We graded the severity of asthma symptoms and the requirement for antiasthma medications at the time of diagnosis and at the time of follow-up visit. Spirometry and measurement of airway responsiveness to methacholine (PC20 methacholine) were also done on both visits. The increase or decrease in asthma symptoms, medications requirement, FEV1 and PC20 methacholine between the follow-up and the diagnostic visit were used to determine the outcome of the patients. Using these parameters, 10.4% of patients improved, 62.5% remained stable, 37.5% deteriorated, and none recovered. Among the characteristics of the patients observed at the time of diagnosis, the age of the patient, the atopic status, smoking habit, and the presence of specific IgE to plicatic acid were not useful in predicting the eventual outcome. Reduction of exposure by transfer to a less dusty job and the use of an airstream helmet did not prevent deterioration of asthma. Only the use of the twin-cartridge respirator was associated with a favorable outcome. We conclude that among cedar asthmatics who remained exposed to cedar dust for an average of 6.5 yr, over one-third showed marked deterioration of their asthma symptoms. There is also no way to predict who will deteriorate. A decrease in the amount of exposure to cedar dust does not prevent deterioration of asthma. This suggests that the ideal management of cedar asthma is removal from exposure.