Background In 2015, the Dutch government implemented a long-term care (LTC) reform primarily designed to promote older adults to age-in-place. Increased proportions of older adults living in the community might have resulted in more and longer acute hospitalisations. The aims of this study were to evaluate whether the Dutch 2015 LTC reform was associated with immediate and longitudinal increases in the monthly rate of acute clinical hospitalisation and monthly average hospital length of stay (LOS) in adults aged 65 years or older. Methods In this interrupted time series analysis of national hospital data (2009–18), we evaluated the association of the Dutch 2015 LTC reform with the monthly rate of acute clinical hospitalisation and monthly average LOS for older adults (aged ≥65 years). Patient-level episodic hospital data were provided by Dutch Hospital Data. Records were included that were defined as an acute clinical hospital admission for which a medical specialist decided treatment was necessary within 24 h. The analysis controlled for population growth (Dutch population data was provided by Statistics Netherlands) and seasonality, and calculated adjusted incident rate ratios (IRR). Findings Before the 2015 LTC reform, the rate of acute monthly hospitalisation was increasing (IRR 1·002 [95% CI 1·001–1·002]). A positive average reform effect was observed (1·116 [1·070–1·165]), accompanied by a negative change in trend (0·997 [0·996–0·998]) that resulted in a decreasing trend over the post-reform period (0·998 [0·998–0·999]). The pre-reform trend of LOS was decreasing (0·998 [0·997–0·998]), and the 2015 reform exhibited a positive change in trend (1·002 [1·002–1·003]) that resulted in a stabilisation of LOS in the post-reform period (0·999 [0·999–1·000]). Interpretation Our findings suggest that the increase in the rate of acute hospitalisation after the reform implementation was temporary, whereas the increase in LOS post-reform appeared to last longer than expected. These results have the potential to inform ...