Patellid limpets are common occupants of mid-shore tidepools on northern European shores, but their tidepool population structures have not been examined in detail. A series of mid-shore tidepools on Clare Island, Western Ireland were cleared of all Patella ulyssiponensis, Gmelin and P. vulgata L., in each of three years. A subset of these pools was subsequently recleared at monthly intervals, to determine juvenile recruitment to the pools and the rates of adult immigration. P. vulgata juveniles (<3 mm) were recruited in much greater densities than those of P. ulyssiponensis, but there was a steady decline of the P. vulgata recruits over time. The majority of limpets in the largest size class (>20 mm) were P. ulyssiponensis. No difference between the two species was observed in the immigration rates of the adults to the pools, but it is suggested that while P. ulyssiponensis remains in the pools, P. vulgata uses this microhabitat solely as a nursery ground, migrating from the pools as the animals increase in size, to give the observed pattern in population structure.