Ascochyta lentis var. lathyri is described for the first time infecting grasspea (Lathyrus sativus L.) in Italy. This fungus causes necrotic lesions on leaves and stems of grasspea plants. Fungal isolates obtained from these lesions were able to infect grasspea under controlled environmental conditions and induced symptoms similar to those observed in the field. Moreover, these isolates were not pathogenic to seedlings of nine other leguminous species including lentil. Sequence analysis of the nuclear ribosomal internal transcribed spacer, as well as fast-evolving protein-coding loci chitin synthase, translation elongation factor 1-alpha, glyceraldehyde-3-phosphate dehydrogenase, revealed 99.6% to 100% similarity to sequences from Ascochyta lentis Vassiljevsky. Morphological analyses using elliptic fourier analysis and MANOVA demonstrated that conidial dimensions of the grasspea fungus were significantly different from those of A. lentis. Crosses between the grasspea fungus and A. lentis were successful and produced progeny with normal cultural morphology and growth rates. Hybrid status of the progeny was confirmed by segregation of mating type and microsatellite markers. These results indicate that the fungus infecting grasspea is a pathogenic and morphological variant of Ascochyta lentis and should be named Ascochyta lentis var. lathyri.