Objectives Continuity of care is a core dimension of primary care, and better continuity is associated with better patient outcomes. Therefore, care fragmentation can be an indicator to assess the quality of primary care, especially in countries without formal gatekeeping system, such as Japan. Thus, this study aimed to describe care fragmentation among older adults in an ageing city in Japan.

Design Cross-sectional study.

Setting The most populated basic municipality in Japan.

Participants Older adults aged 75 years and older.

Interventions This study used a health claims database, including older adults who visited medical facilities at least four times a year in an urban city in Japan. The Fragmentation of Care Index (FCI) was used as an indicator of fragmentation. The FCI was developed from the Continuity of Care Index and is based on the total number of visits, different institutions visited and proportion of visits to each institution. We employed Tobit regression analysis to examine the association between the FCI and age, sex, type of insurance and most frequently visited facility.

Results The total number of participants was 413 600. The median age of the study population was 81 years, and 41.6% were men. The study population visited an average of 3.42 clinics/hospitals, and the maximum number of visited institutions was 20. The proportion of patients with FCI >0 was 85.0%, with a mean of 0.583. Multivariable analysis showed that patients receiving public assistance had a lower FCI compared with patients not receiving public assistance, with a coefficient of 0.137.

Conclusions To our knowledge, this is the first study to demonstrate care fragmentation in Japan. Over 80% of the participants visited two or more medical facilities, and their mean FCI was 0.583. The FCI could be a basic indicator for assessing the quality of primary care.