This study was conducted to determine the relationship between the adherence to treatment and social support in psychiatric patients. The study was completed with a total of 324 psychiatric patients. The data gathering tools used were Demographics Questionnaire, Morisky Medication Adherence Scale and Multi-Dimensional Scale of Perceived Social Support. The study sample consisted of psychiatric patients who were selected from the population by using the simple random sampling method. Among the patients, 50.9% adhered to the treatment, and 14.5% did not. Patients living in city and country-town, with high income and living with family were found to have more social support. A positive, significant relationship was found among scales (p < 0.05). As the mean scores of social support increased, patients' adherence to treatment increased.