The stigmatizing effects of negative expectancies were examined in observations of interactions between children with and without a behavior problem. Ss were 68 pairs of unacquainted boys in Grades 3–6. In each dyad, a normal boy was either told that his partner had a behavior problem or given no expectancy; this expectancy manipulation was crossed with the partner's actual diagnostic status with respect to hyperactivity. The perceivers' expectancy that their partner had a behavior problem as well as the actual diagnostic status of the target adversely affected the boys' interactions. Behavioral data suggest how the expectancies were communicated to the target. The processes underlying interpersonal expectancy effects and the ways in which a childhood stigma can act as a self-fulfilling prophecy are discussed.