Ambiguity, typically characterized as imprecision in judged probabilities, is distinguishable from that uncertainty typically measured using probabilities. It reflects the inadequacy of a point probability judgment and the assumptions upon which it is based. Ambiguity influences both patients’ and physicians’ decisions, but it is unknown how decision makers conceptualize ambiguity. Toward this goal, properties of three ambiguity indicators were examined: A confidence rating, a plausible range, and an interquartile range. Board-certified internists and fourth-year medical students evaluated simulated cases of suspected coronary artery disease. Their judgments provided insights into the three ambiguity indicators. The distri bution-based interquartile range was largely redundant with the plausible range, and was least adequate. The confidence rating was not equivalent to the plausible range, and ap peared to best reflect the construct of ambiguity as it has been defined. Key words: Ambiguity; probability judgments; decision making. (Med Decis Making 1989;9:116-124).