Problem statement:Smoking plays a significant role in the development of periodontal disease. Quantitative relation between smoking and increased severity of periodontal disease, by means of biochemical marker has not been described in Malaysian population. The present study was designed to apply serum cotinine measurement as a quantitative method to evaluate smoking levels in Malaysian patients and to correlate these levels with the severity of periodontal disease. Approach: The study group consisted of 80 healthy individuals (20-64) year, Current Smokers 26, Non Smokers 27 and Former Smokers 27. The subjects were then asked to complete a questionnaire including the demographic, socioeconomic status, medical history and history of cigarette smoking. The periodontal variables recorded were amount of Visible Plaque score, gingival bleeding Index and community periodontal index. Samples of blood "10 mL" were obtained in vacutainer tubes containing EDTA for quantitative analysis of serum levels of cotinine. The serum samples were analyzed for cotinine content by means of a competitive-inhibition ELISA technique. Results: Current smokers represent the highest mean cotinine serum level, 95.5 ng mL −1 , compared to former smokers, 35.5 ng mL −1 and non smokers, 22.9 ng mL −1 . The mean serum cotinine level in periodontally healthy patient showed the highest cotinine level (84 ng mL −1 ) followed by the gingivitis patients (68 ng mL −1 ) and (50 ng mL −1 ) for periodontitis patients. Conclusion: The present observations clearly indicate an association between smoking, periodontal disease clinical parameters "plaque, gingival bleeding scores" and cotinine serum levels in current smokers. Cotinine serum levels doesn't affected by the existence or the severity of periodontal disease.