Implicit attitudes are automatically activated evaluative impulses that are difficult to control and potentially outside conscious awareness. The association of implicit attitudes toward psychiatric medication with treatment adherence and insight was investigated in 85 persons with schizophrenia, schizoaffective, or affective disorders using the Brief Implicit Association Test. Explicit attitudes, insight, perceived need for treatment and adherence were measured by self-report. Implicit, but not explicit, positive attitudes predicted increased insight and perceived need for treatment. Explicit, but not implicit, positive attitudes predicted self-reported adherence. Implicit measures can improve our understanding of medication attitudes and evaluation of interventions to increase treatment adherence.