Japan has universal health insurance and its total health expenditure as a percentage of the gross domestic product is almost 50% less than that of the United States where 15% of persons under age 65 are uninsured. The health of the Japanese population as judged by neonatal, postnatal, and total infant mortality, percent of infants born with birth weights below 2500 g, and life expectancy at birth and ages 20 and 65 is superior to the health of Americans. Primary care, however, as an academic discipline and primary care training programs are absent in Japan. Physician training, incongruent with need, combined with government controlled low professional medical fees contribute to an extraordinarily high annual ambulatory patient contact rate (14 compared with 2.8 for Americans) and excessive use of diagnostic testing. Although primary care training is better developed in the U.S.A., interest in receiving, such training among medical school graduates is declining. Several factors that contribute to quality of care are examined. Comparisons between countries, however, must be viewed with caution because of the multitude of demographic, genetic, historical, economic and cultural variables that influence how health care is delivered and received. Both countries face major challenges. The projected rapid increase in the relative ratio of the elderly to total population in Japan will severely strain its ability to contain health care costs. Interest in primary care training in Japan dates back to 1978 but its implementation has been largely unsuccessful. The challenges in the U.S.A. are far more formidable.(ABSTRACT TRUNCATED AT 250 WORDS)