A new body called Tourism Ireland, funded jointly by the British and Irish Governments, has been set up to promote tourism for the entire island of Ireland. This study investigates whether such an initiative is mutually beneficial for the Republic of Ireland (ROI) and Northern Ireland (NI). It is argued that joint promotion of the island is viable only if interregional tourism demand spillovers are generated. A spillover arises when tourists who visit the ROI also visit NI, and vice versa. The interconnectedness between the two regions' long-haul visitor demand was investigated empirically and it was found that spillovers are significant, albeit asymmetric. NI tourism demand rises 3.2% for every 10% increase in ROI tourism demand, while the latter increases 1.1% for every 10% increase in NI demand.