 All subjects will undergo spirometry, diffusing capacity and quantitative CT scanning. These measurements will allow us to determine differences in the prevalence of emphysema in HIV and HIV- and determine risk factors associated with emphysema. For longitudinal studies testing the hypothesis that emphysema is accelerated in HIV infection, we will select HIV and HIV- subjects with documented emphysema in each group as defined by diffusing capacity80 predicted, post-bronchodilator FEV1FVC70 without significant reversibility, or at least 10 of lung with a density less than -910 Hounsfield units HU. These subjects will have CT scans and PFTs at baseline and at 18 months and 36 months after baseline. At each visit, clinical data and biological samples will be collected. 