To assess the health and cost effects of a patient's risk-taking attitudes about diagnostic tests. Cost-effectiveness analysis. Diagnostic testing strategies used in the evaluation of a patient with a radiographically detected lung lesion were evaluated. Strategies included combinations of sputum, fine-needle aspiration, bronchoscopy, thoracoscopy, and expectant management. Patient data were obtained from the Survival Epidemiology and End Results Program, MEDLINE search, National Center for Health Statistics, and the Universities of Iowa and Stanford, and Kaiser Permanente Hospital. Different patient risk-taking attitudes were simulated using decision analysis. Lifetime cost of medical care, life expectancy, and cost effectiveness. The cost effectiveness of competing strategies depended on patient attitudes about taking risks. For a patient averse to expectantly waiting without definitive knowledge of whether cancer was or was not present, testing strategies using invasive procedures, such as thoracoscopy, were more cost effective. In contrast, for a patient who was identical except that he or she was averse to tests with higher morbidity and mortality, strategies that involved expectantly waiting, instead of more invasive tests, were more cost effective. Small changes in some risk-taking attitudes resulted in large changes in cost effectiveness. Risk-taking attitudes influenced the cost effectiveness of testing strategies. Consideration of patient risk-taking attitudes in diagnostic testing appears warranted in setting clinical policies and making individual decisions.