The study observed population of 484 generation restrictive genealogies collected in four Croatian regions during 1970/71 within "The study of fat and carbohydrate metabolism indicators correlated with the occurrence of diabetes in animal fat and oil consuming population groups". The genealogies were collected on two islands (Brac and Hvar) and in two continental regions (Sinjska Krajina and Srijem). Genealogy Structure Index (GSI) was defined as quantitative indicator of genealogy structure. GSI was continuos variable which, by its extreme, describes vertical and horizontal type of genealogy structure, independently of the way genealogies were collected. Genealogy structure of surveyed population was described on the basis of participation of different genealogy types. Populations of the island Hvar and Brac showed to have horizontal genealogy type, continental population of Sinjska Krajina showed to have mixed type and continental population of Srijem showed to have vertical type of genealogy structure.