The first Swiss mammography screening pilot programme operated between 1993 and 1998. Approximately 15000 women aged 50-69 years and residing in western Switzerland (canton of Vaud) were offered a biennial screening. Quality standard recommendations for screening were met for most performance indicators. Some 4.6%/2.3% (prevalent/incident round) of participants were referred for further assessment, and 84.7%/75.6% of them turned out not to have cancer. Specificity was high (96.1%/98.2%) and the cancer detection rate amounted to 7.0/1000 and 5.9/1000 in the prevalent and incident rounds, respectively. Some 30%/26% of cancers in screened women were interval cancers, which were at a more advanced stage than screen-detected tumours. Screening performances improved with time and age. The objectives of feasibility and acceptability of an organised mammography screening programme in the liberal Swiss healthcare system, where routine opportunistic screening existed, were achieved and contributed to the implementation of screening programmes in two additional Swiss cantons. [authors]