Rainfall-runoff models have received a great deal of attention by researchers in the last decades. However, the analysis of their reliability and uncertainty has not been treated as thoroughly. In the present study, a technique for assessing the uncertainty of rainfall-runoff simulations is presented that makes use of a meta-Gaussian approach in order to estimate the probability distribution of the model error conditioned by the simulated river flow. The proposed technique is applied to the case study of an Italian river basin, for which the confidence limits of simulated river flows are derived and compared with the respective actual observations.