With the increasing installation of wind farms, the attention of citizens towards wind turbine noise (WTN) has grown. Differently from some national legislations, the scientific community has promptly responded, increasing the studies and the social surveys in order to better understand the cause of disturbance and the indicators that relate to it. At first, the paper underlines the importance of low WTN levels for indirect health effects such as sleep disturbance and annoyance. The importance to consider noise annoyance in legislation is also discussed, as WTN is more disturbing than other most common noise sources. Then, conversion curves for equally highly annoyed are introduced considering the annoyance perceived by population in relation with the type of source. Finally, a specific limit value of 43 dB(A) for WTN is derived and suggested, comparable with British and Danish standards.