 Subjects will be 300 HIV subjects and 300 HIV- controls selected by random sampling stratified by age and smoking history. Subjects will be recruited from the University of Pittsburgh and the University of California Los Angles UCLA MACS sites. The University of California San Francisco UCSF will serve as the recruiting center for the WIHS cohort. Because we are interested in an unbiased estimate of the extent of this disease in HIV infection, we will not select subjects based on lung function or current diagnosis of COPD. The HIV- subjects will be matched to the HIV subjects in terms of age and smoking history to the extent possible. Those with symptoms of acute respiratory disease such as fevers, acute change in cough or shortness of breath, or weight loss will be excluded. There will be no exclusions based on HAART use or opportunistic infection OI prophylaxis and no exclusions based on previous lung disease as we are trying to obtain a comprehensive evaluation of emphysema in this population as well as identify associated risk factors. 