Mean pulmonary artery pressure (PAP) has been demonstrated to correlate with measures of pulmonary artery size. We tested the hypothesis that residence at elevated altitudes, a determinant of mean PAP, can be associated with increases in pulmonary artery size on chest radiographs from healthy adults. The study population consisted of three groups of asymptomatic, nonsmoking adults without hazardous respiratory exposures living at altitudes approximating 0 m (group 1, n = 197), 1,400 m (group 2, n = 145), and 2,600 m above sea level (group 3, n = 196). The width of the right descending pulmonary artery (RDPA) was measured at its widest diameter before bifurcation. In a multivariate regression model, significant associations were detected between RDPA width and residence at elevated altitudes (F = 13.84, p = 0.0002), age (F = 32.49, p < 0.0001), and gender (F = 56.10, p < 0.0001), with 36% of the variability of the measure determined by these three variables (r2 = 0.36). Mean RDPA width increased as altitude at residence increased. Larger mean values were noted among older individuals and males. We conclude that residence at altitudes of 1,400 and 2,600 m above sea level is associated with increases in pulmonary artery size on chest radiograph.