Sweden started several large mammography screening trials in the late 1970’s, and in 1986 they started a nation-wide screening programme for breast cancer. Norway started mammography screening in 1996.

All women aged 50-69 years are invited to mammography screening in both countries. In addition, about 50% of women aged 40-49 and 70-74 years are invited to mammography screening in Sweden. Opportunistic screening was frequent in the capital area of Norway (Oslo and Akershus county) before 1996 (where about 20% of the population lives).

More than 92% of women aged 50-69 years have been invited to screening since 1991 in Sweden, and about 40% of women in Norway were invited to mammography screening in Norway in the period 1996-99.

The annual increase in breast cancer incidence was less than 1% before the mid 1970 in Sweden. After the mid 1970’s the breast cancer incidence increased more than 1% annually and the incidence increase was mainly in the age group invited to screening in Sweden. At the same the annual increase in breast cancer incidence in Norway was less than 1%. Norway started mammography 10 years after Sweden. The incidence increases in first, second and third screening round were 82%, 54% and 56%, respectively.