Erodium paularense Fern. Gonz. & Izco (Geraniaceae) is a perennial, endemic species of central Spain. The restricted distribution of its three populations has made it necessary to consider measures for conservation. Random amplified polymorphic DNA markers were used to determine genetic variation among and within populations. Sixty-three per cent of the bands were polymorphic. No population-specific marker was identified. Cluster analysis based on Jaccard's coefficient of all the individuals grouped most of them according to the present populations. Within-population variability was of a similar order in the three populations. Highly significant genetic differences between populations were detected through AMOVA. Within population diversity contributed 80–85% to the species diversity, a value typical of an outbreeding plant.