A female who first acquired pulmonary tuberculosis in 1962 when she was 25 years old, admitted to the National Hiroshima Hospital in 1982. Her sputum has been smear positive for acid-fast bacilli for 3 years before admission in spite of continuous antituberculous chemotherapy, and were resistant to isoniazid (INH) and rifampicin (RFP). She was treated with a regimen containing ethambutol (EB), prothionamide (TH) and enviomycin (EVM) but continued to be culture positive. Though she was treated with various regimens which include one to three sensitive drugs, her sputum continued to be positive for M. tuberculosis in the following 14 years. During the course, resistance to EB, TH, cycloserine (CS) and streptomycin (SM) emerged. Resistance to RFP temporarily retracted in 1988, but her sputum was bacilli negative only for 2 months after the addition of RFP to previous regimen, and followed by resurgence of RFP resistance. In 1992, data of drug sensitivity tests showed sensitivity to TH, CS and RFP in turn, which were not used for 3 to 5 years. In 1993, she was treated with RFP, TH and EVM successfully and continued to be bacteriologically negative for 7 years so far. Drug resistance to M. tuberculosis is induced by inappropriate chemotherapy as seen in this case. Regimens with less than three drugs without RFP and INH was not only insufficient to get cure but, what was worse, also induced additional resistance to used drugs. The reason of successful chemotherapy in this case was spontaneous disappearance of drug resistance to RFP and TH. This case suggests that the disappearance of drug resistance is possible, when drugs are not used for more than a few years, hence the successful treatment could be expected. However it must be emphasized that the drug resistance is produced by incorrect treatment as seen in this case, and its prevention is of the prime importance.