We study the dielectric constant of a fluid of hard spheres with a polarizable point dipole and quadrupole at their center. The deviations from the Clausius–Mossotti formula are found at six volume fractions by computer simulation of a system with periodic boundary conditions. For small polarizability the deviation agrees well with the theoretical result up to a volume fraction of 30%, if calculated in superposition approximation for the triplet distribution function. We also determine the spectral density appearing in the spectral representation of the dielectric constant. The spectrum differs significantly from that for a system with only induced dipole interactions, especially at high volume fraction.