Abstract. In aquatic ecosystems, sediments constitute a reservoir for many of the most persistent chemicals that are introduced into surface waters. Sediments provide a habitat for various benthic macroinvertebrates, which could be exposed to sediment-associated chemicals both directly and via food intake. These organisms play an important role on the structure and the functioning of aquatic ecosystems. Among the non-biologically essential metals, data concerning uranium (U) fate and effects on freshwater benthic macroinvertebrates are sparse. The present study aimed at estimating effects of a chronic U exposure on Chironomus riparius larvae. To achieve this goal, a 10-d laboratory bioassay was performed exposing, via the sediment, first instar larvae to a gradient of U concentrations (0, 2.97, 6.07, 11.44, 23.84 µg U/g dry wt). Significant negative effects on mortality, development time and growth were detected at 6.07, 6.07 and 2.97 µg U/g dry wt, respectively. The results underlined a possible impact of U at the population level at environmentally occurring U concentrations. This study confirmed the need for more research on the role of U on benthic macroinvertebrate.