The current taxonomy of leucocytozoids (Haemosporida, Leucocytozoidae) is based on the morphology of blood stages of the parasites and on limited information about their specificity. Recent molecular studies have revealed a remarkable genetic diversity of leucocytozoids, indicating that their taxonomic diversity may be greater than in the current classifications. We addressed this issue using morphological data and phylogenetic analysis of the cytochrome b gene of 14 positively identified species of avian haemosporidians. Based on the current taxonomy, Leucocytozoon toddi is the sole species of leucocytozoids parasitizing falconiform birds. However, several distinct haplotypes have been revealed in falconiform birds, suggesting that L. toddi might be a group of cryptic species. We investigated the morphology of blood stages of leucocytozoids of 2 haplotypes (2 lineages from Accipiter spp. and 3 lineages from Buteo spp.) and concluded that these parasites can be readily distinguished due to length of the cytoplasmic processes of their host cells; therefore, they do represent distinct morphospecies. Morphology of the cytoplasmic processes of host cells warrants more attention in the taxonomy of Leucocytozoon species. Leucocytozoon toddi indeed is a species group that currently includes Leucocytozoon mathisi, Leucocytozoon buteonis, and L. toddi; additional morphospecies can be added to this group in the future. It is probable that some other morphospecies of Leucocytozoon also might be groups of closely related species.