High coverage is essential for an effective screening programme. Here we present screening barriers and facilitators among 1.3 million women aged 25–69 years eligible for screening within the Norwegian Cervical Cancer Screening Program (NCCSP). We defined non-adherence as no screening test in 2008–2012. We divided adherent women into those screened spontaneously, and those who had a smear after receiving a reminder from the NCCSP. Explanatory variables were extracted from several nationwide registers, and modelled by modified Poisson regression. In total, 34% of women were non-adherent. 31% of native Norwegians were non-adherent, compared to 50% of immigrants. Immigrant status was a strong predictor of non-adherence, but the vast majority of non-adherent women were still native Norwegians. Higher non-adherence rates were associated with having a male general practitioner (GP), a foreign GP, a young GP, and distance to the screening site. Being unmarried, having no children, having lower socioeconomic position and region of residence predicted non-adherence and, to a smaller extent, reminded adherence to screening. In contrast, previous experience with cervical abnormalities substantially increased adherence to screening. The population-based screening programme promotes equity by recruiting women who are less likely to participate spontaneously. However, socioeconomic disparities were evident in a country with a nationwide programme and a policy of equal access to health care. Initiatives aimed at removing practical and financial barriers to equitable screening delivery and at reducing the effect of sociodemographic attributes on screening participation are needed.