The most common explanation for Japan's increasingly low rates of postwar violent crime is the cultural characteristics that exert powerful informal social controls on behavior at the macro level, which suggests low levels of social disorganization. Other explanations for the low levels of violent crime are a low degree of economic stress, a small proportion of young males, and a criminal justice system that ensures a high certainty of punishment. The annual time-series data from 1951 to 2000 were analyzed for the impact of changes in measures of social disorganization, economic stress, certainty of punishment, and young male population on changes in violent-crime rates. The crime measures were homicide and robbery rates per 100,000 residents. Social disorganization was measured by divorce, the female labor force participation, and urbanization. Economic stress was determined by calculating a Gini coefficient of income inequality, the unemployment rate, and the monthly average of persons who were receiving public assistance. The certainty of punishment was determined through total clearance rates. The size of the young male population was calculated as the number of men ages 20-29 divided by the total population. The second part of the study computed prefectural levels of homicide and robbery rates per 100,000 population for 1955, 1960, and 1965, using National Police Agency data and the Japanese Statistical Yearbooks. The pooled time-series analysis used the same independent variables as the annual time-series analysis, except for measures of poverty. The findings from the two analyses were largely in agreement. They showed that measures of economic stress, certainty of punishment, and age structure of the population were, compared to common social disorganization measures, more consistent predictors of Japan's postwar violent crime trends. This suggests that the significant and widespread strength of the postwar Japanese economy may have had a larger role in low violent crime rates than is usually recognized. 5 figures, 2 tables, and 82 references