Active cocaine abusers have a diminished neural response to errors, particularly in the anterior cingulate cortex thought critical to error processing. The inability to detect, or adjust performance following errors has been linked to clinical symptoms including the loss of insight and perseverative behavior. We investigated the cognitive implications of this diminished error-related activity, using response inhibition tasks that required error awareness and performance adaptation. Twenty-one active cocaine users (six female subjects, mean age=40.3) and 22 non-drug using adults (six female subjects, mean=39.9) participated. The results indicated that cocaine users consistently demonstrated poorer inhibitory control, a deficit accompanied by reduced awareness of errors. Adaptation of post-error reaction times did not differ between groups, although a different measure of adaptive behavior: exerting inhibitory control on the trial immediately after failing to inhibit, was significantly poorer in the cocaine using sample. In summary, cocaine users demonstrated a diminished capacity for monitoring their behavior, but were able to perform post-error adjustment to processes not already suffering an underlying deficit. These difficulties are consistent with previous reports of cocaine-related hypoactivity in the neural system underlying cognitive control, and highlight the potential for cognitive dysfunction to manifest as behavioral deficits that likely contribute to the maintenance of drug dependence.