The unconscious thought effect refers to improved judgments and decisions after a period of distraction. The authors studied the unconscious thought effect in a complex and error-prone part of clinical decision making: diagnosis. Their aim was to test whether conscious versus unconscious processing influenced diagnosis of psychiatric cases. They used case descriptions from the DSM-IV casebook. Half of the participants were randomly assigned to the conscious-processing-condition (i.e., consciously thinking about the information they read in the case description), the other half to the unconscious-processing condition (i.e., performing an unrelated distracter task). The main dependent measure was the total number of correct classifications. Compared to conscious processing, unconscious processing significantly increased the number of correct classifications. The results show the potential merits of unconscious processing in diagnostic decision making.