The statistical analysis in this paper concerns the evaluation of the extreme wave return periods on the Italian coasts and the calculation of the average duration of sea storms based on data collected by Italian marine measurement network Rete Ondametrica Nazionale. Ten years of wave data from 8 buoys were analysed following the standard statistical methods recommended by the Working Group on Extreme Wave Statistics - IAHR. Evaluations are based on the estimate of statistical distributions for the extreme wave episodes. Hypotheses of data independence and stationarity were discussed; independent episodes were extracted from the 10-year time series taking into account the directional characteristics of the Italian wave climate. Statistical models were applied in order to obtain return values of significant wave heights corresponding to return periods ranging from 5 to 50 years. The results were analysed and, in order to test the robustness of the analysis, return values for the 5-year return period were compared with observations. Sensitivity to the total number of selected episodes was explored and possible effects resulting from missing storms shown and discussed. An estimate of the mean wave duration was made, based on the evaluation of the statistical model for the probability of exceeding a threshold. A simple power-law formula was found to summarise the results.