ABSTRACT Background: tobacco smoking has been considered a risk factor for obstructive airway diseases, insulin resistance and development of type 2 diabetes mellitus (DM). Aim: to assess the effects of cigarette smoking on lung functions and glucose metabolism in asymptomatic current cigarettes smokers. Methodology: this case-control study was conducted on 100 asymptomatic current cigarette smokers and 100 age and sex matched lifelong non-smokers. Data regarding age, sex, smoking history including age of starting, smoking index and smoking duration were recorded. Spirometric-indices (VC %, FVC%,, FEV1 %,FEV₁/FVC ratio, FEF25-75%), serum fasting plasma glucose mg/dl (FPG) and glycated hemoglobin % (HbA₁C%) were measured. Results: obstructive ventilatory defect and small airways obstruction were significantly higher in asymptomatic smokers than non-smokers (21% vs. 7% and 42% vs. 10% respectively) (p 0.004 and 0.001 respectively). Among smokers the frequencies of the pre-DM and DM detected by FPG there were higher than non-smokers (41% vs. 9% and 10% vs. 1% respectively). Moreover, there was higher frequencies of pre-DM and DM detected by HbA₁C among smokers compared to non-smokers (60% vs. 11% and 10% vs. 1% respectively) (p 0.001). In smokers group both FEV₁/FVC and FEF25-75% was positively correlated with age of starting smoking /yrs (p 0.001), and negatively correlated with smoking index, smoking duration, FPG and HbA₁C (p 0.001). The HbA₁C was positively correlated with smoking index and smoking duration and negatively correlated with age of starting smoking/yrs (p˂ 0.05). Smokers have 17.1 more risk of developing DM, 3.5 more risk of developing obstructive ventilatory defects and 6.5 more risk of developing small airways obstruction compared to non-smokers. Conclusion: smoking is a risk factor for development of DM, obstructive ventilatory defect and small airways obstruction. Both reduced ventilatory functions and increased FPG and HbA₁C negatively affected each other's.