In Japan, The Mycobacteriosis Research Group at the Japanese National Chest Hospitals has continuously made the clinico-epidemiological study of nontuberculous mycobacteriosis (NTM) since early 1970s. The prevalence rate was determined as 0.82, 0.91, 1.22, 1.74 and 2.43 per 100,000 population per year in 1971, 1975, 1980, 1985 and in 1990 respectively. The newest datum in 1997 was 3.52. These data indicates the prevalence rate has continuously increased and became 3.8 times than 25 years ago. While on the other hand, the prevalence rate of lung tuberculosis has decreased from 133.1 to 15.2, becoming one nines in the same period. The numbers of newly detected patients of lung mycobacteriosis in 1996 were also studied at 12 hospitals in Kinki district. The rate of NTM was 16.6% in 4 sanatorium hospitals, being about the same to the datum of The Mycobacteriosis Research Group. The rate of NTM in 8 general hospitals was surprisingly high, 40.0%. The 70% of NTM patients were infected with Mycobacterium avium complex (MAC). The 24% were with M. kansasii, and the only 6% were with other miscellaneous species. That is, the about one thirds or more of total NTM patients were female MAC desease patients, another one thirds or less were male MAC patients, and the more than 90% of M. kansasii patients (about one fourth of total patients) were male. These 3 groups took the most part of NTM patients. The rate of female MAC patients with small non-cavitary lesion without underlying diseases showed a tendency to increase, and the rate of male MAC patients with cavitary lesions with underlying lung or systemic diseases decreased. In 1997, American Thoracic Society (ATS) published the official statement about the diagnosis and treatment of NTM disease. The table-1 in that statement showed the new criteria for diagnosis of NTM pulmonary disease. It is useful for precise diagnosis of lung NTM disease, and the old criteria made by The Mycobacteriosis Research Group of the Japanese National Chest Hospitals is also useful for rough diagnosis. In the ATS statement, for adult HIV-negative MAC patients, minimum three drug regimen of clarithromycin (or azithromycin), rifabutin (or rifampin) and ethambutol, with intermittent streptomycin which is option for extensive disease, is recommended. This regimen is the same that most of the Japanese specialists for NTM disease recommended. The follow-up study of 47 Japanese MAC patients treated by the regimen contained clarithromycin with other anti-tuberculous drugs revealed that 80% of cases converted into bacilli negative and that the regimen had durable effect for at least 24 months. The resectional surgery may be considered for localized disease, and supportive nutritional treatment must also be considered for the MAC patients to whom the drug therapy was not effective, as if for the tuberculosis patients of multi-drug resistant.