The aim of the study is to pres ent the oc cur rence of land slides on the sub ma rine slope of a sandy bar rier. The scale and signif i cance of this phe nom e non is dis cussed. The study area is the Hel Pen in sula. It is a 35 km long young sandy spit. The landform is prograding into the deep part of Gdańsk Bay, and the un der wa ter ex ten sion of its tip is a steep sandy slope. The tip is still poorly in ves ti gated, as it was a mil i tary area closed to re search ers un til 2003. The first de tailed sur vey of the tip on the sea bed was con ducted aboard the re search ves sel “IMOR”. A multibeam echosounder, a sub-bot tom profiler and a side-scan so nar were used, while grab and core sam ples of sed i ment were ob tained. Many forms, com monly cre ated as the re sult of un der wa ter mass move ment, were rec og nized and de ter mined (main scarps, main bod ies, land slide steps, landslide foots, se ries of small slides,“sheet” slides and struc tural slides). On the one hand, the land slide pro cesses that oc cur in the tip of the Hel Pen in sula are re lated to the nat u ral de vel op ment of sandy spits. On the other hand, they threaten the shore’s sta bil ity. The gen e sis of the land slides is still not known.