Evaluation of the effect of Papanicolaou screening in Sweden: record linkage between a central screening registry and the National Cancer Registry.

Development of in-situ or invasive carcinoma of the uterine cervix was studied among 930,127 women reported to a Swedish Central Screening Register through a record linkage between that Register and the National Cancer Registry. The relative protection against cervical cancer after one negative smear, calculated on incidence level prior to screening, is 14.5 for the first year and drops to 3.4 five years after the screening. The relative protection after two or more negative smears is considerably higher for the first three years but for the years following drops to the same level as after one negative smear.