Organised mammography screening programmes may reduce socioeconomic inequalities in breast cancer screening, but evidence is contradictory. Switzerland has no national organised mammography screening programme, but regional programmes were progressively introduced since 1999, giving the opportunity to conduct a nationwide quasi-experimental study. We examined the evolution of socioeconomic inequalities in mammography screening in Switzerland and if exposure to regional organised programmes reduced socioeconomic inequalities. Data of 10,927 women aged 50 to 70 years old were collected from the Swiss Health Interview Survey, a nationally representative cross-sectional survey repeated 5 times (1992-2012). Socioeconomic characteristics were assessed using education, income, employment status, and occupational class. Adjusted prevalence ratios of up-to-date mammography screening were estimated with Poisson regressions and weighted for sampling strategy and non-participation bias. In the absence of organised screening programmes (1992-1997), prevalence of mammography screening increased by 23% and was associated with tertiary education and working part time. During the period of progressive introduction of regionally organised programmes (2002-2012), prevalence of mammography screening increased by 19% every 5 years and was associated with exposure to regional programmes and with independent/artisan occupations. Tertiary education and working part time were no longer associated. Exposure to organised programmes did not modify socioeconomic inequalities except for employment status: not employed women benefitted more from organised programmes compared to women working full time. In conclusion, socioeconomic inequalities in mammography screening decreased over time but organised programmes did not greatly modify them, except women not employed whose prevalence passed employed women.