In this paper it is demonstrated that the anisotropy, as measured by Hiraokaet al., in the extraordinary Hall constantR1of nickel can be theoretically predicted but cannot be explained in terms of the anisotropy in the resistivity alone. A quantum calculation, using both the tight‐binding approximation and the Karplus‐Luttinger theory of the extraordinary Hall effect, is performed to show the existence and estimate the magnitude of the anisotropy inR1. The phenomenological equations for the anisotropy in the resistivity, as derived by Do¨ring, are employed to indicate that Hiraoka's experimental results cannot be explained only in terms of the anisotropy in the resistivity measured in the direction of the Hall voltage.