Although there is growing evidence that males tend to suffer higher levels of parasitism-than females, the implications of this for the population dynamics of the host population are not yet understood, Here we build on an established 'two-sex' model and investigate how increased susceptibility to infection in males affects the dynamics, under different Mating systems, We investigate the effect of pathogenic disease at different case mortalities, under both monogamous and polygnous mating systems. If the case mortality is low, then male-biased parasitism appears similar to unbiased parasitism, in terms of its effect on the population dynamics. At higher case mortalities, we identified significant differences between male-biased and unbiased parasitism. A host population may therefore be differentially affected by male-biased and unbiased parasitism. Tha dynamical outcome is likely to depend on a complex interaction between the host's mating system and demography, and the parasite virulence. © 2007 Miller et al.