Four-wave mixing (FWM) is one the limiting factors for existing and future wavelength division multiplexed optical networks. A semianalytical method based on Monte Carlo and Extreme Value theory is proposed and applied to study the influence of the FWM noise on the performance of WDM systems. The statistical behavior of the FWM noise is investigated while the Bit-Error rate is calculated for various combinations of the design parameters and for both single and multiple span WDM systems. The semianalytical method is also compared to the Multicanonical Monte Carlo (MCMC) method showing the same efficiency and accuracy with the former providing however the advantage of deriving closed-form approximations for the cumulative distribution functions of the photocurrents in the mark and the space state and the BER.