The invention relates to methods for monitoring variable speed wind turbines (11), which include a means of control for pitch regulation according to a power vs. speed curve for the turbine (21) as a function of the wind speed expressed by a transference function (TF) applied to the wind speed measured by a wind sensor located where the wind flow is distorted, and which includes the following steps: a) providing a function of the optimum ratio (F1) of a wind speed variable (V) and a wind turbine performance variable (P); b) continuously measuring said variables (V, P) and obtaining a function that is a ratio (F2) thereof; c) continuously obtaining a parameter (D) indicating the differences between said functions (F1, F2); and d) generating a warning message when the value of said parameter (D) is greater than a predetermined value.
