In contingency judgment a primacy effect exists when a conclusion about the relationship between clinical variables is inordinately influenced by cases seen earlier rather than later in a presentation sequence. In this study, medical and nursing trainees evidenced this behavior in a hypothetical clinical judgment situation. The behavior was tied to an attention decrement explanation, by which inattention to the later-presented cases leads to inaccurate recall of the relative frequencies of observed cases, which in turn induces a misjudgment of a disease-finding contingency. An explicit intervention based on this hypothesis, forcing attention to later cases by warning that recall of the case frequencies would be required, was effective in reducing primacy effects among medical students. A related, but less explicit, intervention was also tried. This intervention did not significantly reduce primacy effects among nursing students, but was somewhat effective among general undergraduate students performing a non-clinical contingency judgment task.