Advances in therapy have largely contributed to the increased life expectancy of patients with cystic fibrosis. Unlike children, adults with cystic fibrosis must take responsibility for their own care. We administered a questionnaire to 23 adult patients (aged 18-39 years) with cystic fibrosis to (1) determine patients' degree of compliance with medications and chest physiotherapy; (2) collect information on their self-assessment of health motivation, disease severity, and benefits of treatment; and (3) identify barriers to receiving medical care. Patients reported better compliance with medications than with chest physiotherapy. Nine percent of the patients missed at least 25 percent of prescribed medication, whereas 47 percent missed at least 25 percent of prescribed physiotherapy. We observed a trend toward better compliance in patients who were highly worried about their health, who believed their illness to be serious, and who felt that their medications were very effective. Less than half of the study participants believed physiotherapy to be effective, and that adhering to a physiotherapy schedule was very difficult. Among adults with cystic fibrosis, compliance can be a serious problem that minimizes the benefits of good medical care. We suggest that emphasizing the severity of disease and usefulness of therapy may improve compliance and requires study.