Chronic obstructive pulmonary disease (COPD) is more important as a cause of morbidity than as a cause of mortality but estimates of its frequency and distribution are inadequate and incomplete. According to annual report of World Health Organization, in 1998 there were estimated to be 52.2 millions deaths in the world, among them 2.9 millions were due to respiratory diseases and almost of them were COPD. Estimates of prevalence COPD vary depending on the diagnostic criteria used, the age and sex composition of the population, their exposure to cigarette smoke and possibly to other harmful environmental influences. In the present review, we discuss the problems arising in the data of morbidity and mortality of COPD in Japan.