Background: Many clinicians have experienced the difficulty of decision on termination of antituberculosis chemotherapy after the 6th month due to relapse of disease. There is still controversy in the effect of 2S(K)HRZ/4HRZ 6-month short course chemotherapy including pyrazinamide for 6 months in patients with pulmonary tuberculosis. And there is no long term follow-up study of 6-month short course chemotherapy for pulmonary tuberculosis in korea. So we had performed the study to find the result of 6-month antituberculosis chemotherapy for 4 years. Method: We studied prospectively the effect of 2S(K)HRZ/4HRZ in one hundred-fifty patients with pulmonary tuberculosis and followed up fifty-nine patients for more than 1 year to 4 years after the completion of 6-month short course therapy. Results: 1) Out of one hundred-fifty patients, seventy-two patients(48%) completed the prescribed 6-month chemotherapy. Sixty-eight patients(45.3%) have experienced premature discontinuation and the most common cause of premature discontinuation was drop-out against advice(thirty-six patients, 24%). Ten patients(6.7%) were treated beyond the 6 months mainly due to irregular treatment. 2) Fifty-nine patients(81.9%) among seventy-two patients with completed treatment have been followed up for more than 1 year and 32 patients(44.4%) for more than 4 years. There was three relapse patients of whom two patients have experienced relapse of pulmonary tuberculosis within 1 year after the termination of chemotherapy. 3) Among one hundred-thirty-four patients who have been assessible for more than two months of chemotherapy, including the patients who experienced within 2 months, there were eighty-two patients(61.2%) who have experienced adverse reactions and the treament regimen was changed only in thirteen patients(9.7%). The most frequent cause of adverse reactions was arthralgia and/or hyperuricemia, which had occurred in 33 patients(24.6%). Conclusion: In a university hospital in Korea, 6-month short course chemotherapy of 2S(K)HRZ/4HRZ had unnegligible relapses and premature discontinuation. Therefore, change of the regimen might be carefully considered by drug susceptibility results. Close monitoring of patients, retrial of sputum exam and radiologic evaluation during treatment might be required in the endemic area of drug resistant strains like in Korea. Further study about the effect of 6-month short course chemotherapy including pyrazinamide for 6-month might be needed.