Background: The primary aim of this study was to quantify the degree of non-adherence to medications among patients with mental health disorders attending a psychiatry clinic at a tertiary care hospital in Muscat, Oman.Methods: All patients attending the psychiatry clinic during the study period were invited to participate in this cross-sectional study. Demographic data and factors related to medication adherence were gathered from the participants. The level of adherence to medication was measured using the Medication Adherence Rating Scale (MARS).Results: A total of 251 patients were included in this study. The average MARS score was 5.7, indicating an overall poor level of compliance. Having an educational level of secondary school, a diagnosis of schizophrenia, having had a mental health condition for a longer time, previous history of admission to a psychiatry unit, lack of insight and poor therapeutic alliance were found to be significantly association with low level of adherence to psychiatric medications.Conclusions: Non-adherence to medications is common among patients with mental health disorders. In order to mitigate the impact of medication non-adherence in a psychiatric setting, appropriate interventions are recommended to address and manage the factors related to poor medication adherence.