Background: The Kingdom of Saudi Arabia is in the midst of a diabetes mellitus (DM) epidemic whose origins can be traced to (a) the widespread adoption of the Western diet that is high in sugar, (b) an increase in sedentary activity, and (c) ignorance of the importance of DM. The purpose of this cross-sectional study was to quantify various aspects of (a) knowledge, (b) attitudes, and (c) practice relating to DM. Methods: The three research questions addressed in this study were: (1) Is there any significant relationship between attitudes to DM and practices related to DM? (2) Is there any significant relationship between knowledge of DM and practices related to DM? (3) Is there any significant relationship between knowledge of DM and attitudes to DM? Separate surveys for each question collected data from a representative sample of 1,067 adult both male and female Saudis from Riyadh who have not been diagnosed with DM. Results: Data analysis of the data from the study indicated that for each of the three research questions, the null hypothesis could not be rejected, indicating that none of the relationships were statistically significant. Conclusion: The absence of significance for each of the findings has important implications, including (a) the possibility that many Saudis incorrectly believe themselves to be unsusceptible to DM and (b) the high prevalence of DM-causing behaviors in the Saudi population. These two implications should be of particular concern to public health authorities and health educators in Saudi Arabia, who may need to work more diligently to educate non-DM-diagnosed Saudis on their vulnerability to DM.