In psychiatry, one of the main factors contributing to poor response to pharmacological treatment is adherence. Noncompliance with maintenance treatments for chronic illnesses such as schizophrenia and affective disorders can exceed 50%, Poor adherence can be due to drug-related factors (tolerance, complexity of prescription, side effects, or cost), patient-related variables (illness symptoms, comorbidity, insight capacity, belief system, or sociocultural environment), and physician-related factors (communication or psychoeducational style). Psychosocial treatments must be used in conjunction with medication during the maintenance phase to improve adherence to treatment and to achieve - through the management of psychological variables - better social, work, and family functioning. This article reviews the concepts of adherence and noncompliance, and their impact on maintenance treatments, as well as the effect of dealing with psychosocial factors in psychiatric treatment.