Objectives: To estimate the overall prevalence of psychiatric disorders among prisoners and its associated factors, and to estimate the prevalence of different mental and personality disorders. Methods: This was a cross-sectional descriptive study carried out in 16 randomly selected prisons in Egypt. A stratified proportional random sample of 1350 adult prisoners was included in the study. Data were collected by a psychiatrist by direct interview with prisoners. The study questionnaire obtained information about socio-demographics, prisoner circumstances, medical history, psychological factors, legal history of the prisoner as well as the Arabic version of the Structured Clinical Interview for the DSM-IV Axis I and Axis II disorders. Bivariate and logistic regression analyses were performed to determine the significant factors associated with presence of psychiatric disorder. Results: The overall point prevalence of psychiatric disorders was 22%, excluding substance abuse and alcohol intake. The independent predictors for psychiatric disorders were work in prison (adjusted odds ratio = 0.6), family visits (0.5), substance abuse outside prison (2.7), history of psychiatric disorders outside prison (2.0), and repeated admission to the prison (2.5). The prevalence of mood disorders and psychosis was 3.3% and 1.3%, respectively. The overall prevalence of personality disorders was 13.6%. Conclusions: Psychiatric disorders are prevalent among prisoners; the most common being personality and antisocial disorders. There is a need for psychiatric assessment of prisoners when first imprisoned and for subsequent regular monitoring and treatment.