The influence of the presence of magnetic islands, and the consequentmodification of the tokamak magnetic surface topology, on electroncyclotron current drive is analysed. To this end, a new three-dimensionalFokker-Planck code has been developed, taking into account themodifications of the magnetic equilibrium topology owing to the presence ofthe islands. Significant differences between the electron cyclotron currentdrive efficiency with and without islands inside the plasma are found,particularly in the case of interaction with locked modes.