Veterans with HIV who had a CD4 count lower than 200 cells per μL or of 200–499 cells per μL had a higher risk of pulmonary hypertension than did veterans without HIV (HR 1·94 [1·49–2·54], p<0·0001, for those with <200 cell μL and HR 1·29 [1·08–1·53], p=0·0048, for those with 200–499 cells per μL). The gene discussed is CD4; the disease is pulmonary arterial hypertension.