Bone morphogenetic protein 15 (BMP15) is a member of the transforming growth factor beta superfamily, is specifically expressed in oocytes and is essential for sheep prolificacy. Reported mutations in this gene cause increased ovulation rate and infertility in a dosage-sensitive manner. In this work, a new naturally occurring mutation in the BMP15 gene from the ovine Rasa Aragonesa breed is described. This mutation is a deletion of 17 bp that leads to an altered amino acid sequence and introduces a premature stop codon in the protein. Highly significant associations (P < 0.0001) were found between the estimated breeding value for prolificacy and the genotype of BMP15 in Rasa Aragonesa animals with high and low breeding values for this trait. As for other mutations in BMP15, this new mutation is associated with increased prolificacy and sterility in heterozygous and homozygous ewes respectively.