Background: A range of psychiatric disorders are associated with brain tumors. The aim of this study was to assess the frequency of psychiatric disorders in adults with primary brain tumors before and after surgery. Methods: The study was conducted on 120 adult patients diagnosed with primary brain tumors (age ≥18 years). Patients with recent diagnosis (less than 6 months) who were hospitalized in Imam Reza Hospital of Tabriz between December 2016 and November 2017 were included. The diagnostic interview was performed based on DSM-IV criteria using a semi-structured interview with SCID-I before and one month after surgery. The frequency of psychiatric disorders in patients was then compared pre- and post-operation. Results: Pre-surgical studies revealed that 26.66 % of patients with primary brain tumors had symptoms of psychiatric disorders. The most prevalent disorders found in patients were depressive disorders (13.07 %), adjustment disorder (9/15 %) and anxiety disorders (5.88 %). Post-surgical evaluations indicated that the frequency of psychiatric disorders was reduced to 22.5 %. However, there was no significant difference between pre- and post-surgical outcomes. Among patients with psychiatric disorders, the most common location of brain tumors was frontal lobe and the most common pathology was meningioma. Further analysis also revealed that tumor location and pathology was not associated with the incidence and type of psychiatric disorders. Conclusion: In adults with primary brain tumors, the most common psychiatric disorder was depressive disorder.