Intolerance of ambiguity is the perception of ambiguous situations as threatening. It has often been measured using Budner's 1962 intolerance of ambiguity scale in studies of medical students and physicians. To examine the test-retest reliability of the scale among that population, we administered it to all 171 entering medical students at one medical school immediately prior to beginning classes and readministered it to them six to nine weeks later with an 81% follow-up rate. The Pearson correlation between the first and second administrations was .64, showing moderate reliability during this stressful period in medical socialization. The internal reliability of the scale remained constant; the alpha was .64 at the first administration and .63 at follow-up. These data indicate moderate reliability of Budner's intolerance of ambiguity scale when respondents are medical students.