The thermal stability of stoichiometric spinel phases in the system Li1+deltaMn2-deltaO4 (0 less than or equal to delta less than or equal to 0.33) has been investigated by high-temperature powder X-ray diffraction, differential thermal analysis, and thermogravimetric analysis. At elevated temperatures, the lithium-manganese-oxide spinels undergo phase changes by loss of oxygen and lithia (Li2O). The data highlight the importance of temperature control when synthesising lithium-manganese-oxide spinel compounds.