The aim of this study was to evaluate trends in incidence of breast cancer in women less than 40 years in Asia. Registered cases of female breast cancer age less than 40 years and corresponding person years were ascertained from the CI5plus for 10 registries in Asia for the duration of 1970-2002. Cases were categorized into three age groups: 16-40, 16-29, and 30-40. The 16-40 age group was adjusted to world age population structure. Joinpoint regression analysis was conducted to determine the annual percent of change (APC) and the average annual percent of change (AAPC) for each age group. A total of 23,661 cases of breast cancer occurred in the 10 registries during the 32 years (1970-2002) of follow-up. The overall age adjusted (16-40 group) breast cancer incidence rate increased from 2.28-4.26 cases per 100,000 population corresponding to an AAPC of 2.6%(95% CI 2.1, 3.0). The trend in incidence for the age group 16-29 increased from 0.45-1.07 corresponding to an AAPC of 2.8%(95% CI 1.9, 3.7). In age group 30 to 40, the incidence ranged from 13.3 in year 1970 to 24.8 in year 2002 corresponding to an AAPC of 2.7%(95% CI 2.3, 3.1). There were two statistically significant changing points in the regression line for the age groups 30-40 and 16-40: one point in the year 1975 with an APC of 6.1 (5.1, 7.1), and the other in 1985 with an APC of 0.4%(0.01, 0.8). Our study proved that: 1) the incidence of breast cancer in young women has increased in Asian population during the study period; 2) the rate of increase was very high during the period of 1980-1990.