The invention concerns a rotor blade of a wind power installation, comprising a rotor blade root (4) for attachment of the rotor blade to a rotor hub and a rotor blade tip arranged at a side remote from the rotor blade root, as well as a wind power installation having such rotor blades. In that arrangement a relative profile thickness which is defined as the ratio of profile thickness to profile depth has a local maximum in a central region between rotor blade root and rotor blade tip.