Forty-one cases of progressive systemic sclerosis were reviewed retrospectively in order to ascertain the frequency of roentgenographic pulmonary arterial hypertension (PAH) in progressive systemic sclerosis (PSS). Chest roentgenograms on 12 per cent (5 of 41) of the cases reviewed showed definite or probable roentgenographic evidence of pulmonary arterial hypertension, and a total of 15 (37 per cent) might be inferred to have had pulmonary arterial hypertension by recorded roentgenographic, clinical, and/or pathologic criteria. The degree of pulmonary arterial hypertension was out of proportion to the severity of interstitial pulmonary disease attributable to scleroderma. Moreover, no correlation between the presence or recorded severity of Raynaud's phenomenon and the presence of clinical and/or roentgenographic evidence of pulmonary arterial hypertension was observed. Radiologists should be aware of the possibility of pulmonary arterial hypertension in known cases of progressive systemic sclerosis; in addition, they should be prepared to raise the possibility of this association in the differential diagnosis of roentgenographically evident "idiopathic" pulmonary arterial hypertension.