Objectives　Integrated implementation of health services and long-term care (LTC) prevention for older adults require programs to understand the health status of persons with unknown health status and connect them to appropriate services. Previous studies have suggested that identifying such individuals can predict those at high risk of needing LTC pertaining to care level ≥ 2 or death; however, the relationship with frailty remains unclear. This cross-sectional study aimed to examine the association between individuals with unknown health status identified using the National Health Insurance (KDB) system and corresponding frailty.Methods　We used response data from the LTC Prevention Questionnaire (an all-inclusive survey conducted in 2020 targeting older adults aged ≥65 years who were not certified as requiring LTC in Yamato City, Japan). The analysis included 16,186 older adults aged ≥76 years. They were divided into two groups: "unknowns" (those who did not receive medical checkups or medical care in 2019-2020) and "knowns" (those who received medical checkups or medical care in 2019-2020). Univariate analysis and multivariate logistic regression analysis were performed for frailty (at risk for ≥8 items) in the Kihon Checklist and the applicable criteria for each field, and odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for each.Results　The OR for frailty was 1.58 (95% CI: 1.21-2.07), which was statistically significant and higher among those who had been unknown health status for two consecutive years, even after adjustment for sex, age group, and family structure. The adjusted OR for each criterion in the Kihon Checklist was 2.26 (95% CI: 1.55-3.30), which was the highest for "prevention/support for homebound" among those who were unknown for two consecutive years. Statistically significant associations were found for "20 items except five related to prevention/support for depression" and "improvement of motor functions."Conclusion　Frailty was significantly associated with individuals aged ≥76 years who had not received health checkups or medical care for two consecutive years and were not certified as requiring LTC. In programs for understanding the status of persons with unknown health status and connecting them to appropriate services, it is considered necessary to actively implement measures against frailty, not just to recommend that such individuals receive health checkups and medical care.