The carbon-13 chemical shift data for a series of 1,7-dioxa-, 1-oxa-7-thia-, and 1,7-dithiaspiro[5,5]undecanes and related compounds are presented. Analysis of this data led to structural and stereochemical assignments. The results show that the unsubstituted spiro bicyclic compounds exist in the conformation shown as conformationa. It is shown that the13C chemical shift parameters developed for cyclohexane derivatives can be applied to the sulfur but not to the oxygen heterocycles.