ABSTRACT RATIONALE, AIMS AND OBJECTIVES: Against the background of a general rise in the incidence of breast cancer temporal variations appear in different age groups, including changes attributable to the introduction of breast screening. This paper attempts to distinguish the influence of breast screening and to examine any underlying patterns. The incidence data published by the Office of National Statistics for England and Wales have been examined using the method of least squares regression. These data have been subjected to major revision: a new system was introduced in 1971. That year, therefore, has been taken as the starting point for the analyses. Regression lines were fitted from 1971, 1984 and 1988 (when breast screening was started). Results Between 1971 and 1984 breast cancer incidence was unchanged in women under 50 years. In all other age groups and time periods the incidence has risen throughout 1971-1999. The rate of increase remained constant for women over 64 but changed in 1984 for all women under 65 years. The rate of increase is rising exponentially with age since 1984 in the women under 65. The superimposed increases due to screening have been separated from the underlying rates. In the period surveyed there appears to have been a change in the rates of increase in incidence of breast cancer in women under 65 that dates from 1984. This change can be separated from the spurious increase due to breast screening. The rates in women over 64 have remained constant.