To determine the association between mitral regurgitation and pulmonary edema localized in the right upper lobe, the authors reviewed 21 cases of mitral regurgitation secondary to dysfunction or rupture of the papillary muscle or rupture of the chordae tendineae cordis. The patients, 12 men and 9 women ranging in age from 36 to 92 (mean 64) years, had been admitted to a tertiary care hospital between July 1985 and July 1990. Three independent observers, who were unaware of the patients' identity or the diagnoses, reviewed the chest radiographs. In eight of the patients pulmonary edema was localized preferentially in the right upper lobe, an unusual pattern that can simulate neoplasia, hemorrhage or infection. All eight patients had myocardial infarction, five had papillary muscle dysfunction, and three had rupture of the posterior papillary muscle. Mitral regurgitation toward the orifices of the veins of the right upper lobe seems to play a role in the preferential distribution of edema to that lobe. Awareness of edema in the right upper lobe in association with mitral regurgitation might lead to earlier diagnosis of papillary rupture or dysfunction and perhaps affect the outcome.