The influence of “seasonality” on the distribution of maxima of a hydrological variable has been studied theoretically and through examples relating to flood discharges of three Italian rivers. Results obtained lead to the conclusions that: (a) The shape of the distribution function of annual extremes is not related to that of the seasonal components which determine it. In particular it is not stable (extreme values asymptotic distribution) even if the components are stable. This property weakens all the more the reasons for the preference usually given to these distributions. (b) In addition, the analysis of seasonal maxima does not seem to be useful for increasing the reliability of estimates of rare events. In fact, the observations available in addition to the analysis of only the annual maxima, are, by their nature, found mostly in the range of small discharges. Therefore these additional observations produce more noise than information and often cause notable errors even in the range of the largest discharges observed.