The linear coefficient of thermal expansion of semiconducting Hg1−xCdxTe has been determined for alloy compositionsx= 0.20 and 0.30, of interest to infrared detector technology. The temperature dependence is similar to that of other compounds of zinc blende structure. The thermal expansion coefficient becomes negative at 64 K and is insensitive to composition except below 30 K, where the alloys richer in HgTe exhibit a deeper negative minimum.