Marine protected areas are expected to play a prominent role in the conservation of marine resources and fisheries management. In the Basque Country (northern Spain) the small Marine Reserve of Gaztelugatxe (158 ha) was established in 1998. One of the aspects taken into account in protecting this area was the overexploitation of the goose barnacle Pollicipes pollicipes. Now, after five years of protection, differences in density, biomass, size and weight of the goose barnacle are investigated inside the protected area (Aketze and Gaztelugatxe locations) and outside of it, at the nearest locations (Izaro and Ogoño) which have been continuously exploited. This contribution demonstrates that the reserve could be an efficient tool in preserving the goose barnacle populations in the area. Hence, density, biomass and allometric coefficients are higher in the protected areas. These locations are also associated with higher percentages of juveniles, together with a high number of large-sized individuals.