A variety of slope failure features have been identified in the vicinity of the Hellenic arc. In prodelta environments small‐scale block slumps are the predominant products of shelf instabilities on relatively low angle slopes (0.5–2°), while relatively larger scale rotational and translational sides, as well as debris and turbidity flows, were observed on steeper slopes (2–8°). The shear plane is believed to be the gas‐charged sediments and/or the fine‐grained (and low shear strength) basal sedimentary layer of the prodelta sediment sequences. A series of rotational slide blocks were also observed within the shelf‐edge Late Pleistocene prodelta sequence. These failures were initiated soon after the sequence was deposited but are presently inactive. Large‐scale translational slides and slumps were detected, particularly in the fore‐arc continental slopes, associated with major active fault zones. Pleistocene interglacial hemipelagic mud sheets or sapropelic layers may act as failure planes within these slopes. Cyclic loading induced by earthquake activity is the principal cause of the undrained slope failures in the investigated area of the northeastern Mediterranean Sea. Storm‐wave loading or tsunamis could be additional factors for inducing failure of the upper slope, particularly during low sea‐level stands. Infinite‐slope stability analysis indicates that, in general, slopes greater than I ° are unstable in areas in which the expected peak ground accelerations exceed 13–15% g.