Ischia is a volcanic island located at the margin of the Gulf of Naples in the southeastern Tyrrhenian Sea, Italy. In this article, we investigate the stability of the deep‐seated block known as Mt. Nuovo in the northwestern flank of the Mt. Epomeo volcano under a combined gravitational and seismic load. Mt. Nuovo is bounded by a number of active seismic faults and is placed close to the epicentral area of the 1883 Casamicciola earthquake (IMCS=X, Mw 5.8), that is, the largest shock occurring in the island in historical times. We explore the hypothesis that a Casamicciola‐like earthquake might occur with an epicenter in the Mt. Nuovo block area. Using relationships between maximum seismic intensity and peak ground acceleration found in the literature as well as a new relationship derived specifically for this study, we apply the minimum lithostatic deviation method, which is a variant of the limit‐equilibrium method, to assess the stability of the block. The main finding is that Mt. Nuovo would be mobilized if such an earthquake took place on a fault very close to the block, which would give rise to a catastrophic mass failure and to a disastrous tsunami. This calls for the need of continuous monitoring of the volcano seismicity and deformation pattern.