  M. Lapidus and C. Pomerance (1990-1993) and K.J. Falconer (1995) proved that
a self-similar fractal in $\mathbb{R}$ is Minkowski-measurable iff it is of
non-lattice type. D. Gatzouras (1999) proved that a self-similar fractal in
$\mathbb{R}^d$ is Minkowski measurable if it is of non-lattice type (though the
actual computation of the content is intractable with his approach) and
conjectured that it is not Minkowski measurable if it is of lattice type. Under
mild conditions we prove this conjecture and in the non-lattice case we improve
his result in the sense that we express the content of the fractal in terms of
the residue of the associated $\zeta$-function at the Minkowski-dimension.
