The primary mechanism by which cocaine induces stereotypy has been difficult to discern because cocaine has three high-affinity targets: the reuptake transporters for dopamine (DAT), norepinephrine, and serotonin. To dissect out the role of DAT in cocaine effects, we generated a knock-in mouse line with a cocaine-insensitive DAT (DAT-CI mice). DAT-CI mice provide a powerful tool that can directly test whether DAT inhibition is important for cocaine-induced stereotypy. We found that acute cocaine failed to produce stereotypy in DAT-CI mice. In fact, 40 mg/kg cocaine suppressed stereotypy in DAT-CI mice but produced profound stereotypy in wild-type mice. These findings suggest that DAT inhibition is necessary for cocaine-induced stereotypy. Furthermore, mechanisms independent of DAT inhibition appear to inhibit stereotypy.