Rainfall-runoff models are frequently used by hydrologists to estimate runoff from rainfall and climate data, with the model adequacy assessed by comparing the level of agreement between flows simulated by the model and the recorded flows. This paper describes simple methods (visual plots, statistical parameters and dimensionless coefficients) which are commonly used to compare estimated and recorded streamflow time series and discusses their advantages and limitations. Results of a survey conducted to ascertain the required quality of flow estimates before they are considered to be satisfactory, as well as to identify preferred methods used by hydrologists in Australia to determine the adequacy of streamflow estimates, are also discussed in this paper. Information from the survey is also used to suggest objective criteria based on dimensionless coefficients that can be used as guides in assessing the adequacy of flows estimated by rainfall-runoff models. In particular, the coefficient of efficiency is a very useful indicator in assessing model adequacy.