A population of the Iberian endemic rodent, Cabrera vole Microtus cabrerae Thomas, 1906, was monitored from April 1997 to April 1999 in monthly trapping sessions. Results suggest that low rainfall combined with high temperatures is a limiting factor for reproduction in this population. Population density (17-115 ind/ha) was lower than values recorded for most Microtus species, and similar to those recorded for certain species living in atypical habitats or for non-cyclic microtines. The total value of recruitment (55.8%) was lower than for other Microtus, attributable to the weather, litter size, monogamy, and territoriality. Persistence and residency were higher than in other species of Microtus; such values in M. cabrerae could be due to its slower rate of renewal, characteristic of the K-strategy of reproduction. Habitat patch size correlated with reproductive variables, but not with presence/absence of individuals. The minimum area to consider a patch as a source was 300 m2; smaller patches showed non-continuous occupation, lower number of breeding pairs, and scarce number of young born. Habitat fragmentation at the local level, in addition to human activities in rural areas, may worsen the effects of climatic fluctuations in Cabrera vole habitats, leading to a decrease of patch size and therefore of the ability to sustain populations.