Raffaella Servadei and Enrico Valdinoci Fractional Laplacian equations with critical Sobolev exponent (65K, LaTeX) ABSTRACT. In this paper we complete the study of the following elliptic equation driven by a general non-local integrodifferential operator~$\mathcal L_K$ $$\left\{ egin{array}{ll} \mathcal L_K u+\lambda u+|u|^{2^*-2}u+f(x, u)=0 & \mbox{in } \Omega\ u=0 & \mbox{in } \RR^n\setminus \Omega\,. \end{array} ight.$$