Patterns of chironomid species richness were compared between 1 permanent and 1 temporary Mediterranean mountain stream in the same basin. From 1991 to 1995, pupal exuviae were collected at irregular intervals in the permanent stream, but the temporary stream was dry because of a long-lasting drought in the region. From March 1996 to March 2000, pupal exuviae were collected fortnightly in both streams. In contrast to other comparative studies that found more species in permanent than in temporary streams, our 2 streams harbored similar temporal γ and α diversity during the 1996 to 2000 study period. This result might be explained by the relatively long time the temporary stream was flowing. In addition, the temporary stream showed higher temporal β diversity than the permanent stream, a result that might be attributable to the greater variability in temperature and substrates in the temporary stream. Spates scarcely affected α diversity and favored colonization by new species in both streams, a result that supports the patch-dynamic concept of streams. A period of >1 y without spates also resulted in colonization by new species in the permanent stream, but led to a pool phase in the temporary stream that reduced α diversity considerably. Overall, both streams had similar chironomid species richness and species rarity and high faunal complementarity. These results support the view that temporary aquatic habitats deserve consideration in conservation plans designed to protect species and their habitats.