Three main sources of error are appointed concerning the use of₁₃ C-analyses of human skeletons in the study of early diet. These are specific to the Baltic: 1) The Baltic exchanges water with the North Atlantic, although not in sufficient amounts to obtain the same₁₃C content.Moreover this exchange has varied with time; 2) The ₁₃C content has perhaps not been the same throughout the Baltic. 3) Some species of marine animals migrate within or out and into the Baltic. In spite of the difficulties these erros create, some differences between coastal and inland samples are demonstrated for prehistoric and medieval time. -- AATA