Some studies found an association between obesity and increased cervical cancer risk, but potential mechanisms are unknown. In this nationwide register-based cohort study, we investigated the association between overweight/obesity and cervical cancer screening participation and risk of unsatisfactory smears. The study population was identified in the Danish Medical Birth Registry. We included 342,526 women aged 23-49 years with pre-pregnancy body mass index (BMI) registered during 2004-2013. Screening participation and unsatisfactory smears during up to four years after child birth were identified in a nationwide pathology register. We used absolute risk regression to estimate the relative absolute risk (RAR) with 95% confidence intervals (CIs) of screening participation according to BMI, adjusted for age, calendar year, sociodemographic characteristics, parity and previous high-grade cervical intraepithelial neoplasia. Among those who were screened (n = 295,482), we used log-binomial regression to investigate the relative risk (RR) of an unsatisfactory smear according to BMI, adjusted for age, year, parity, oral contraceptive use and pathology department. A lower proportion of obese women (79.3%) than women of normal weight (85.8%) were screened, and obese women had lower adjusted probability of being screened than women of normal weight (RAR(adjusted) = 0.94, 95% CI, 0.93-0.95). A higher proportion of obese women (2.4%) than women of normal weight (1.7%) had an unsatisfactory smear, and this association remained after adjustments (RRadjusted = 1.28, 95% CI, 1.19-1.38). In conclusion, women with obesity were less likely to participate in cervical cancer screening and more likely to have an unsatisfactory smear than women of normal weight.