In this study, trends in hospital use were identified in Japanese cities. Data for all inpatient care in May 1985 (9,555 patients) and in May 1988 (11,205 patients) paid for by National Health Insurance in 12 cities in Osaka Prefecture were analyzed. The main factor affecting differences in inpatient days per insured person of all ages (hospital use) among the cities were differences in hospital use by long-stay patients aged 70 years or older, which depended not on inpatient days per patient but on the rate of hospital admission. The main factor affecting change in mean hospital use from May 1985 to May 1988 seemed to be an increase in hospital use by long-stay patients 70 years of age or older, which did not depend on increases in the rate of hospital admission, but did depend on the number of insured persons 70 years of age or older. Calculation showed that an increase of 13 long-stay patients 70 years of age or older for 10,000 insured persons 70 years of age or older per year was to have accounted for about 40% of the increase in hospital use by all patients. If the trend for increasing hospital use in Japan is to be altered, the first step might be the careful planning for this comparatively small increase in long-stay elderly patients by promotion of a non-hospital-based care system.