jats:pIn the absence of written records, disease and parasite loads are often used as indicators of sanitation in past populations. Here, the authors adopt the novel approach of integrating the bioarchaeological analysis of cesspits in an area of medieval Leiden (the Netherlands) with historical property records to explore living conditions. Using light microscopy and enzyme-linked immunosorbent assays (ELISA) they identify evidence of parasites associated with ineffective sanitation (whipworm, roundworm and the protozoan jats:italicGiardia duodenalis</jats:italic>)—at residences of all social levels—and the consumption of infected livestock and freshwater fish (Diphyllobothriidae, cf. jats:italicEchinostoma</jats:italic> sp., cf. jats:italicFasciola hepatica</jats:italic> and jats:italicDicrocoelium</jats:italic> sp.).</jats:p>