This review of the Finnish Disease Heritage (FDH), a group of rare hereditary diseases that are overrepresented in Finland, includes the following topics: FDH characteristics, causes and background, primary theory, revis(it)ed theory, consanguineous marriages in Finland, internal migration of the 1500s, family series for further FDH studies, geography and population structure as a basis for FDH, geography of individual diseases, the structure of FDH families, family structure in individual diseases, Finnish gene mutations, linkage disequilibrium and haplotypes, age of gene mutations, frequencies of disease genes and carriers, and a short description of the possible future of FDH.