Diabetes mellitus occurs when the blood glucose is too high because of the human body’s inability to make insulin at all or is insufficient at making insulin. Increasing patient knowledge of diabetes mellitus leads to increased patient compliance in treatment and collaboration in care plan decision making. There were no known studies regarding the knowledge, attitudes, and practices of Saudi Arabian patients prior to this study. The objective of the present study was to assess and document the level of knowledge, attitudes, and practices of diabetic patients’ regarding diabetes mellitus, its complications, and its management. This cross-sectional design was conducted with 906 Saudi Arabian diabetic patients from endocrinology outpatient clinics in 47 hospitals in 8 cities. Self-report pen and paper study was used to obtain results, which were inserted to Excel and transferred to SPSS for analysis. Saudi diabetic patients do not have significant knowledge regarding diabetes mellitus, but are knowledgeable regarding the implications of diabetes mellitus and precautions against diabetes mellitus. This information cannot be generalized outside of Saudi Arabia, yet can be used to inform health care providers in other countries regarding their own diabetic patients, which may impact the self-management of their diseases.