It is gradually becoming recognized that mental disorders are a public health problem throughout the world. Psychiatric epidemiological studies are therefore crucial for the planning and development of psychiatric services. Objectives: To determine the prevalence and determinants of mental illness morbidity among adult attending PHCCs in Baghdad. Methods: A cross sectional survey was conducted in two primary health care centers in Baghdad governorate. Participants were interviewed and data filled using a questionnaire for sociodemographic variables. Self-Reporting Questionnaire, and WHO guide to mental health in primary care. Results: A total of 527 were approached. The prevalence of mental illnesses was 36.8%. Depression (49.48%) and anxiety (20.62%) were the major categories of mental illness. The highest proportion of mental illnesses was among the older age groups (80%), female (37.9%), widows (84.6%), higher education level (96.7%) and retired (77.8%). Conclusion: In accordance with other studies, about one third of adult attending PHCCs had mental disorders. The study emphasized strengthening mental health services in PHCCs through establishing metal health care units.