An epidemiological study of the relationship between obesity and fatty liver of students in Japan was performed. Measurements of subcutaneous fatty tissue (Nagamine's method) and body weight (according to the Ministry of Health and Welfare 1971-standard body weight method and 1986-standard body weight method) were used to determine obesity. The data of 6,485 18-year-old male and female students of Okayama University, obtained from records beginning 30 years ago, and the data of 1,932 students, obtained in 1986, were examined. The frequency of obesity of men increased since the nineteen-seventies (10.8% in 1986), but that of women did not change for the past 30 years. However, the frequency of emaciation of women has increased for the past 5-6 years (11.5-10.0%). Male students with negative HBs-antigen, higher GPT levels than GOT levels with one or both levels being abnormal, and high choline-esterase level (△ pH over 1.10) were suspected of having fatty liver, and many of them (85.7% by Nagamine's method, 66.7% by 1971-standard body weight method and 71.4% by 1986-method) were diagnosed as being obese. The students with fatty liver (judged by echography) had a greater frequency of obesity (86.7% by Nagamine's method, 80.0% by 1971-method and 76.7% by 1986-method) than those without fatty liver. The measurement of subcutaneous fatty tissue (Nagamine's method) was useful for screening fatty liver in students.