The order-disorder phase transition of tetrathioorthoesters of the elements of group IV with the general formula X(SCH3)(4) and X = C, Si, Ge, Sn was studied by differential thermal analysis, X-ray diffraction, and H-1 NMR measurements. Whereas a disordered phase was observed in a broad temperature range for C(SCH3)(4), this phase gradually decreases with increasing radius of the central atom. No disordered phase was observed for Sn(SCH3)(4). A model for the completely ordered and partially disordered phases of C(SCH3)(4) is proposed.