Twenty-five male volunteers underwent chest radiography at 550 m above sea level (baseline) and at 4,559 m at 6, 18, and 42 hours after arrival. Nine had a history of high-altitude pulmonary edema (HAPE). Starting by 6 hours and independent of the consecutive presence of HAPE, the diameters of the central pulmonary arteries increased by 10%-30% at 4,559 m. At 18 hours and, increasingly, at 42 hours, radiographic evidence of HAPE developed in eight subjects: six with previously documented HAPE and two without. Radiographic signs of HAPE were most severe peripherally, and morphologic characteristics were compatible with permeability and/or overperfusion edema and normal pulmonary venous pressure. Extensive radiographic findings were accompanied by discrete pulmonary rales, and chest radiography proved valuable in detecting HAPE in subjects with normal findings of lung auscultation. This study demonstrates a significant individual susceptibility of lowland residents with a history of HAPE to develop HAPE, resulting in a recurrence rate of 66%.