We investigated the course of adherence to medication recommendations in 162 patients with psychotic disorders in ambulatory treatment. Data were collected using the clinic's outcome assessment program, maximizing the generalizability of the study. Patients initially adherent to their medication regimens maintained their adherence for an average of 13.3 months. Patients initially nonadherent developed adherence after an average of 5.6 months of treatment. Demographic factors and illness history were unrelated to adherence. This study replicated previous findings of the concurrent association between adherence and global functioning level, substance use, and working alliance with therapist. Cox regression analyses revealed that working alliance, global functioning, and being prescribed clozapine predicted longer maintenance of adherence. Working alliance was the most significant and consistent predictor of adherence to medication recommendations.