In this paper, we will give necessary and sufficient conditions for the Hurwitz stability of MIMO interval systems. As a consequence of this result, we will give a precise bound on the H-infinity norm of unstructured perturbations that can be tolerated by MIMO interval systems connected in feedback with these perturbations. We will also consider the robust version of the Popov problem that considers interval MIMO systems subject to nonlinear time invariant sector bounded perturbations and, in turn, obtain a robust stability condition of the Popov problem with mixed perturbations.