Rhizocephalan cirripedes are a very unique group of parasites infecting decapod crustaceans but apart from a few well-studied species little is known on their ecology and impact on hosts. Here we report on the results of a 14 month study of infestations of the rhizocephalan Parasacculina leptodiae in the rocky shore crab Leptodius exaratus along the shores of Kuwait in the Persian (Arabian) Gulf. Monthly samples along an intertidal gradient revealed a slightly higher prevalence of P. leptodiae in female (18%) compared to male crabs (11%) and marked differences in prevalence among the sampling sites. Crabs from more sheltered locations in Kuwait Bay showed lower prevalence of P. leptodiae compared to crabs from more exposed sites. Seasonal patterns were largely absent but prevalence in female crabs showed some monthly variation depending on the site. Rhizocephalan prevalence was generally highest in both crab sexes at the lower shores. This possibly resulted from lower exposure of crabs to infective stages in the higher intertidal and movements of infected crabs to lower parts of the shore. Prevalence of ovigerous females significantly declined with increasing local parasite prevalence. This suggests that the well-known castrating effects of rhizocephalans on individual hosts can also affect local crab reproduction at the population level which has not been shown before. Our results indicate that the rhizocephalan P. leptodiae is a common parasite of the rocky shore crab L. exaratus along the shores of Kuwait, with potential effects on the crab’s population dynamics which warrants further study.