Secale vavilovii PMCs have more univalents and a lower frequency of bound arms at metaphase I than other diploid Secale species. The spreading technique applied at prophase I showed that the nuclei were able to complete synapsis at pachytene. However, 25% of the nuclei analyzed, which had more than 90% of their total length paired, showed two abnormalities: long fold-back loops, which were located mainly on the nucleolar organizer bivalent, and pairing-partner switches, probably involving all the chromosome complement. These synaptic abnormalities are unusual in diploid species and give rise to a high frequency of nonhomologous pairing regions and, therefore, could produce desynapsis, which could explain the data obtained from metaphase I. The possible origin of the unusual synaptic abnormalities of S. vavilovii is discussed.Key words: S. vavilovii, synaptonemal complex, spreading, synaptic abnormalities.