Pulmonary alveolar proteinosis is a relatively rare, diffuse lung disease for which whole lung bronchopulmonary lavage is an effective treatment. The possibility of spontaneous remission also exists, but few actual cases have been described. This report describes a 56-year-old woman in whom pulmonary alveolar proteinosis was diagnosed 18 years earlier and who had a prolonged spontaneous remission before presenting with disabling symptoms. The possibility of prolonged spontaneous remission, although unusual, needs to be kept in mind when therapeutic decisions are to be made in patients with pulmonary alveolar proteinosis.