For the purpose of clarifying functions expected of primary care physicians (PC physicians) in Japan, a study of the types and frequencies of health problems seen in primary care clinics located in three areas, together with consultation/referral rates of the patients to other institutes. The study was conducted using ICHPPC-2 (Japan version) which had been compiled by WONCA as a classification of diseases. In order to obtain much more generalized characteristics of the primary care, clinics located in the city, suburban district and remote places in the mountains were studied. The results were as follows: 1) The health problems treated by the clinics in each of the three areas were respectively: 162 types/7,207 items/4 months: 303 types/17,519 items/2 years: and 280 types/61,916 items/2 years. 2) The consultation/referral rates were under 2%. 3) PC physicians treated over 98% of the health problems encountered. This was found by the investigation, which had been intended to disclose a range of so-called COMMON DISEASES treated by PC physicians themselves, based on a relation between the referral rates and the types of health problems. The above findings suggested that the COMMON DISEASES should include at least 95% of the health problems which had been treated by the PC physicians. This corresponded to approximately 100 types of diseases.