  Relativistic formulas for the electric quadrupole moment of a hydrogenlike
atom, induced by the hyperfine interaction, are derived for $ns_{1/2}$ and
$np_{1/2}$ states. Both the magnetic dipole and electric quadrupole hyperfine
interactions are taken into account. The formulas are valid for ions with
arbitrary nuclear charge and spin. The induced quadrupole moment is compared
with the nuclear quadrupole moment for a wide range of hydrogenlike ions.
