ImportanceHuman papillomavirus (HPV) self-sampling addresses barriers to cervical cancer screening, and mailed self-sampling kits have been reported to increase screening uptake. International research suggests mailed kits are cost-effective in certain settings. However, the cost-effectiveness of mailing HPV self-sampling kits for increasing screening uptake has not been evaluated in the US.ObjectiveTo conduct an economic evaluation of a mailed HPV self-sampling intervention among underscreened women enrolled in an integrated US health care system.Design, Setting, and ParticipantsThis economic evaluation involved a cost-effectiveness analysis of results from a randomized clinical trial of 19 851 women aged 30 to 64 years enrolled in a health plan from Kaiser Permanente Washington (KPWA), a US-based integrated health care system. Women were identified through electronic medical records, and eligible participants were enrolled in a health plan for at least 3 years and 5 months, had a primary care clinician, had not received a Papanicolaou test for at least 3 years and 5 months, and had not received a hysterectomy. Enrollment occurred from February 25, 2014, to August 29, 2016, with follow-up through February 25, 2018. The current economic evaluation was conducted between August 2, 2021, and July 30, 2022. Intervention delivery costs were calculated from both the KPWA and Medicare perspectives and were based on either wellness visit or Papanicolaou test–only visit costs.InterventionParticipants in the control group received usual care, which comprised patient reminders and ad hoc outreach for screening. Participants in the intervention group received usual care plus a mailed HPV self-sampling kit.Main Outcome and MeasuresThe primary economic outcome was the incremental cost-effectiveness ratio (ICER) for increased screening uptake, defined as the incremental difference in cost (intervention group minus control group) divided by the difference in the number of participants completing screening (intervention group minus control group) within 6 months of randomization.ResultsAmong 19 851 women (mean [SD] age, 50.1 [9.5] years; 76.7% White), 9960 were randomized to the intervention group, and 9891 were randomized to the control group. Baseline ICERs ranged from $85.84 (95% CI, $85.68-$85.99) using KPWA wellness visits as the cost basis to $146.29 (95% CI, $146.20-$146.38) using Medicare Papanicolaou test–only visits as the cost source. Subgroups of participants aged 50 to 64 years and participants most recently overdue for screening achieved cost-effectiveness at lower levels of willingness to pay for an additional completed screening than other subgroups.Conclusions and RelevanceIn this economic evaluation, mailing HPV self-sampling kits to women overdue for cervical cancer screening was cost-effective for increased screening uptake relative to usual care. These results support mailing HPV kits as an efficient outreach strategy for increasing screening rates among eligible women in US health care systems.