The present study describes findings in relation to perceived body size and 'desire for thinness' by age and residential areas ('metropolitan areas', 'large cities', 'small cities' and 'towns') among young Japanese women. Data on 1731 non-pregnant, non-lactating women aged 15-39 years from the 1998 National Nutrition Survey of Japan were used. Current body size was evaluated by BMI percentiles (lean, <5th; underweight, 5th or = BMI <25th; normal, 25th< or = BMI< 75th; overweight, 75th < or =BMI <95th; obese, > or =95th), calculated for 5-year age groups. Perceived body size was obtained by self-report. We defined 'overestimation' as non-overweight, non-obese women who perceived themselves as being 'overweight' or 'obese'. Desired body size was evaluated by applying the desired BMI to these cut-off points. Of all the women, 48.4% perceived themselves as being 'overweight' or 'obese', and 43.7% desired a 'lean' or 'underweight' body size. Adjusted for the current BMI, the OR for 'overestimation' calculated by a logistic regression model was significantly elevated in the 15-19-year age group (OR 2.79; 95% CI 1.76, 4.43), compared with the 25-29-year age group. The OR for 'desire for thinness' was significantly high in the 35-39-year age group (OR 2.74; 95% CI 1.93, 3.89) and the 15-19-year age group (OR 2.26; 95% CI 1.57, 3.24). Women living in metropolitan areas had higher OR for 'desire for thinness' (but not for 'overestimation') than did women in towns (OR 1.47; 95% CI 1.05, 2.07). The findings suggest the nature of excessive weight concerns of young women in Japan; thus efforts to control such health-risk behaviours at a national level are urgent.