In the paper the relationship between the yearly maxima of the peak discharge Q and the mean daily discharge q with the same return period is examined, analyzing the data relevant to the Po basin stations. The analysis shows that the relationship can be assumed to be linear and the ratio R between Q and q can either increase or decrease as the return period increases. The effect exercised on R by the main basin hydrological and geomorphological characteristics is also analyzed. It turns out that R decreases with the return period when the basin is very large and the q variability, represented by the variation coefficient, is high.