Background: Poor & non-adherence to medications are serious issues in the management of chronic diseases such as diabetes mellitus. Amounting body of evidence indicates that decreased medication adherence is associated with increased rate of hospitalization and total costs of care. Objective: For studying the prevalence of drug non-adherence & poor/ partial adherence among adults and its associated risk factors totaling with causes. Patients and Methods: Prospective descriptive cross sectional study was carried out in Azadi Teaching Hospital at Kirkuk Governorate of Iraq. Based on the inclusion and exclusion criteria 500 patients were enrolled into study, which had Diabetes Mellitus. Results: Five hundred adult patients participated in this study. Estimated mean prevalence rate of drug non-adherence were: (1) self-perceived adverse effect of medicines (16.67); (2) complicated medicine regimens (7.07); (3) inadequate knowledge about medicines and diseases(1.01);(4) frightening from dependency and addiction (3.54); (5) the stigmatization (4.54); (6) drugs not present in health centers (16.67); (7) considering disease is transient and not lifelong (8.58); (8) considering the drug is not effective (18.18); (9) the cost of medications (21.71); (10) the forgetfulness (2.02). Conclusion: The drug non-adherence is an important concern or problem in a patient management. Medication regimens should be simplified as more as possible, in particular to avoiding cutting pills or using of different dosages at a different timing. Patients should be encouraged to voice out their perceived drug adverse effects. Further worksare needed to determine the prevalence and causes of patients, non-adherence to medication in Kirkuk Governorate.