Patterns of parasite infestation by plerocercoid forms of the tapeworm Ligula intestinalis (Cestoda, Pseudophyllidea) in thesecond intermediate host, the roach Rutilus rutilus, were analysed in three fish populations of South-Western France during1998. In all three studied sites, i.e. Pareloup Lake, Lavernose-Lacasse and Muret gravel pits, roach were commonly parasitizedwith plerocercoids. A strong increase in prevalence, mean number of parasites and parasitic load was observed in the youngesthosts with a maximum peak reached in the medium-age (2+, 3+)roach classes. Such trends as a function of host fish age wouldindicate the occurrence of parasite-induced host mortality, with the most heavily infected fish specimens being removed fromthe three roach populations. The three roach populations infected by L. intestinalis exhibit different patterns of parasite-inducedmortality which could correspond to different possible ecological and evolutionary responses associated with local variation inhost-parasite interactions. The parasite-induced host mortality observed, i.e. direct mortality caused by pathogenic effectsand /or enhanced fish predation by piscivorous birds to increase parasitic transmission is discussed within the context of theadaptative parasite-induced manipulation hypothesis.