Diabetes mellitus is a major public health problem in the Kingdom of Saudi Arabia. Several studies have shown that diabetic patients are at a greater risk of developing oral health problems than non-diabetics. This study aims to evaluate the oral hygiene practices of adult diabetic patients and their awareness of oral health problems related to the disease. In this cross-sectional, Internet-based descriptive study, a self-administered questionnaire was uploaded online and any adult diabetic patient living in Saudi Arabia was allowed to take part. The participants were asked to complete the questionnaire and submit it online. A total of 278 diabetic patients, ranging from 18 to 64 years of age (115 male and 163 female), responded and submitted their questionnaires. In the section on oral hygiene practice, the results showed 45.6% of the respondents brush their teeth once daily, 10.4% floss once daily, and only 11.5% use mouthwash regularly. Regarding patients' awareness, the majority (81%) are aware that diabetes may increase the risk of oral health problems; 75.9% are aware that diabetes may increase the risk for periodontal problems including gum bleeding and teeth mobility and 36.3% are aware that diabetes may reduce salivary flow. The main source of information was the media (31%), followed by dentists and dental hygienists (23%), physicians (21%) and the Internet (16%). Majority of the participants are aware of the importance of controlling diabetes in order to minimize oral health complication (74.4%) but only 15.1% of them visits the dentist regularly. Patients with higher levels of education (graduate and postgraduate) showed statistically significantly better brushing habits and more awareness regarding oral health problems related to diabetes in comparison with those with low levels of education (p value <0.05). Grouping patients by age and gender did not reveal any statistical difference in their level of awareness or brushing habits. Diabetic patients' level of awareness of their increased risk of oral health problems was generally acceptable. Further educational programs should be established for diabetic patients, especially those with low levels of education, in order to improve their oral health knowledge and dentists should take on more responsibility for this task.