Morphology and size of spermatids were analysed in the grasshopper Eyprepocnemis plorans by means of light and electron microscopy. At light microscopy, normal and abnormal (macro- and micro-) spermatids differed in size and number of centriolar adjuncts (CAs): 1 CA in normal spermatids and 2 or more CAs, depending on ploidy level, in macrospermatids. Males carrying the additional B24 chromosome showed significantly more macro- and microspermatids than 0B males. The frequency of macro- and microspermatids showed an odd-even pattern in respect to the number of B chromosomes, with a higher frequency of abnormal spermatids associated with odd B numbers. Transmission electron microscopy showed that macrospermatids carried more than one axoneme, depending on ploidy level: 2 for diploid, 3 for triploid, and 4 for tetraploid spermatids. In 0B males, the most frequent abnormal spermatids were diploid, whereas in 1B males they were the tetraploid spermatids and, to a lesser extent, triploid ones. This suggests that most macrospermatids derived from cytokinesis failure and nucleus restitution. The implications of aberrant spermatids on B chromosome transmission and male fertility are discussed.