Patient mobility is a crucial phenomenon in contexts of hospital competition based on quality and driven by patient choice. This study examines inter-regional patient mobility in the Italian National Health Service, a regionally decentralised tax-funded system in which in-patient hospital services are provided free at any point of use in the whole country, using administrative data on hospital discharges from 2001 to 2010 in all public and private accredited hospitals. The aim is to understand whether mobility patterns might have consequences for the efficiency and effectiveness of the healthcare provided at the regional level, as well as universalism and equity in healthcare. We specify a gravity model for Origin-Destination (OD) flow data that distinguishes between emissiveness (at Origin) and attractiveness (at Destination) factors affecting bilateral flows. We exploit the longitudinal dimension of the data and estimate a negative binomial conditionally correlated random effects (CCRE) dynamic model that allows for region-pair-specific unobservable heterogeneity. Total and specific types of flow (surgical, medical, acute and cancer-related admissions) are modelled, accounting for the correlation between unobserved region-pair effects and time-variant covariates and their spatial lags. Our main findings indicate that RHSs in the richest regions attract more patients from other regions and that the most effective pull factors are the number of beds and diversification of the organisational structure. We also find that the ability of a RHS to attract patients who reside in other regions decreases with the concentration of the organizational structure. Finally, we have detected a mildly explosive dynamics in inter-regional patient mobility over time, which could have implications for the long-run sustainability of the overall national-regional health system.