The family was placed in the larger group Diadectomorpha by paleontologist D.M.S. Watson in 1917, which includes another family of large-bodied diadectomorphs, the Limnoscelidae, as well as the monotypic diadectomorph family Tseajaiidae, represented by the genus "Tseajaia".
The family was placed in the larger group Diadectomorpha by paleontologist D.M.S. Watson in 1917. Diadectidae is closely related to another family of large diadectomorphs, the Limnoscelidae, as well as the monotypic diadectomorph family Tseajaiidae, represented by the genus "Tseajaia".