Objectives: The present study focused on the frequency of Delusional Disorder (DD) in the patients hospitalized in a psychiatric ward in the west part of Iran (Kermanshah), Method: In this retrospective and descriptive research, 601 hospitalized patients' files (1992 to 1996) at Farabi Hospital were inspected. The frequency of the patients with DD, their demographic information, co-morbid somatic complaints with DD, types of delusion, perceptual disturbances, mood state, state of insight and course of illness were studied. Results: Fifty-nine cases (8,9%) were found with the diagnosis of DD. The prevalence of DD was more common among men than women, while the available literature shows the reverse pattern. Conclusion: The results of the present study showed that the characteristics of the DD are somewhat similar to the earlier reports, but the gender and mood state showed noticeable differences.