The incidence rate of breast cancer in the total population increased between 1988 and 1996. The greatest increase was seen after 1993 when population-based screening became available. In unscreened women, modeling demonstrated a statistically significant (p<0.01) 1.5% annual increase in the incidence rate. The annual increase in this rate differed by size of tumor and was approximately 8% (p<0.01) for small tumors (<or = 10 mm) but not significant for tumors>10 mm