This study was conducted to determine the prevalence of mycobacterial disease in an adult cystic fibrosis (CF) population and to determine if there were any patients at higher risk for this disease within the group. Sixty-four patients (28 women, 36 men), ranging in age from 17 to 50 years were screened. One-step purified protein derivative skin testing with controls was performed and sputum was taken for examination. Eight of 64 had positive sputum culture for nontuberculous Mycobacterium. The CF patients with positive mycobacterial sputum cultures tended to be older and to have lower clinical scores than those who did not have Mycobacterium organisms in sputum. Guidelines to determine whether mycobacterial disease or colonization is present should be pursued for the CF population.