Largely unexplained increases in breast cancer incidence of about 1% per year have been documented back to the 1940s. Since 1982, breast cancer incidence in women aged 40 years and above has been increasing at a faster rate than this long-term secular trend, especially in women aged 60 years and above. Increases in the use of mammography since 1982 (which have been documented in population surveys of women) provide the most plausible explanation for the incidence increase over the long-term secular trend. A study by White et al. (J Natl Cancer Inst 1990;82:1546-52) found that, for women aged 45-64 years, the increase in mammography utilization could explain the incidence increase, while for women aged 65-74 years, it could account for only half the increase. The authors have developed an alternative model to that of White et al. that incorporates estimates of differential lead time (time from screen detection to clinical detection in the absence of screening) by age group. Using this model, the authors show that if older women have longer lead times, than similar increases in mammography utilization across age groups will lead to a larger incidence increase in older women. Thus, the observed increases in mammography utilization are generally concordant with increases in incidence, even in the older age groups.