The aim of this study was to investigate the patients' awareness of the effects of smoking on periodontal health in Kingdom of Saudi Arabia (KSA), and to compare with similar studies in UK and Nigeria. This cross-sectional survey was conducted on a convenience sample of 600 patients attending dental clinics of Riyadh Colleges of Dentistry and Pharmacy in 2014 using anonymous, self-completed, questionnaires. The questionnaire included mainly closed-ended questions such as smoking status, duration, frequency, type, level of awareness, and demographics. Descriptive statistics and Chi-square test was performed to analyze the data. 95.7% patients were aware that smoking had a negative impact on oral health. Majority of the patients were aware that smoking causes oral cancer and stains. 11.3% (n=68) stated that smoking affected the gums. Only 4.3% (n=26) of the respondents knew specifically of the link between smoking and periodontal disease. There was a statistically significant relation between awareness of the effects of smoking on oral health with gender, nationality, and smoking status (p < 0.05). This study highlights patients' lack of awareness of the relationship between smoking and periodontal diseases, with only 4.3% of the respondents knowing of the link. This finding closely resembles those of the UK and Nigerian study.