We applied a three-dimensional general ocean and coastal circulation model to the Irish Sea in order to determine water renewal time scales in the region. The model was forced with meteorological data for 1995, a year with relatively warm summer and when extensive hydrographic surveys were conducted in the Irish Sea. We investigated intra-annual variability in the rates of net flow through the Irish Sea and carried out several flushing simulations based on conservative tracer transport. The results indicate that the net northward flow of 2.50 km(3)/d is seasonally highly variable and under certain conditions is reversed to southward. The variability in obtained residence times is high; baroclinic effects are significant. Obtained results point at the importance of spatial and temporal consideration for transport of pollutants in the shelf seas. Implications for management are numerous and involve activities such as transport, fishing, use of resources, nature conservation, monitoring, tourism and recreation. (C) 2009 Elsevier Ltd. All rights reserved.