Introduction: Chronic obstructive pulmonary disease (COPD) is a disorder characterized by maximal expiratory flow decrease and slow forced lung exhalation, which are significantly unchanged over several months. Subjects and Methods: Our study included 100 patients, 50 males and 50 females, diagnosed COPD who have been tested by functional lung tests: spirometry, body plethysmography and blood gas analysis. Patients have been analyzed at Clinic for pulmonary diseases and TBC, University Clinical Center Tuzla. All tests have been done at Department for Cardiorespiratory Diagnostics. Results: In this study have shown highly significant correlation among following parameters: FEV1 and VC, FEV1 and FEF 25, FEV1 and FEF75/25, FEV1 and FEF75, FEF25 and FEF75/25, FEF75 and FEF75/25. In males FEV1, VC and FEV1/VC have been significantly decreased comparing to females. Our results have shown no significant deference among spirometry, plethysmography and blood gas analysis parameters in male smokers with COPD comparing to female smokers. It has been found significant difference for pCO2 in male comparing to female nonsmokers. Conclusion: According to the results we recommend that all individuals having chronic cough, dyspnea and wheezing, and who are smokers or ex-smokers, aged >45 years, considering BMI, should be tested by spirometry.