While there has been a marked decrease in the use of imprisonment in Japan in the post-World War II era, there has been a startling rise in the female incarceration rate. This upsurge is the result primarily of the increase in prison admissions of females convicted of stimulant-drug offenses. The study presents a careful longitudinal analysis of the distribution of other crimes for which women are sent to prison, along with a discussion of sentence length. The article also examines the changing role of women in the Japanese culture. The increased imprisonment rate for women in Japan is a paradox in several senses: (1) It is in sharp contrast to the remarkable decline in the male imprisonment rate; (2) It cannot be attributed to a feminist movement and to women engaging increasingly in "male crimes"; and (3) It has been largely the result of admissions for stimulant-drug offenses, which involve male and female offenders. The article concludes that increased admission of stimulant-drug offenders, in and of itself, is the explanation for the fundamental paradox, not differences between the sexes in trends for length of sentence, age at admission, or previous exposure to imprisonment. Tables, notes, references