The diversity of chironomid larvae in relation to flooding and drought phases in a marginal fluvial wetland of the Middle Paraná River floodplain was analyzed. Four sampling stations in the right bank of the Tiradero Viejo River towards the interior of the marginal wetland were established: one at the riverside, and three more at 10, 30 and 40 m from the river. Bottom sediment samples were extracted during the hydrosedimentological cycle of 2001. A total of 25 taxa of Chironomidae were recorded. The values of taxonomic richness, density and diversity were higher in the marginal fluvial wetland than in the riverside, increasing when the wetland is disconnecting from the river. Polypedilum (Tripodura) spp., Polypedilum (Polypedilum) spp., Ablabesmyia (Karelia) spp., Coelotanypus sp., Monopelopia cf. boliekae, Goeldichironomus holoprasinus and Chironomus gr. decorus spp. were dominant in marginal wetlands. The results indicate that the variations in the hydrosedimentological regime, the degree of disconnection with the river and the progressive desiccation at each one of the stations of the marginal fluvial wetland are limitant factors in the distribution and abundance of aquatic chironomids. The different assemblages of Chironomidae were strongly conditioned by temporal changes related to the gradient of inundation-drought and to the hydroperiod dynamics.