This paper reports a study into the long-term performance of cement stabilized colliery shale. A total of 16 samples were obtained from various UK collieries chosen to provide shales with a representative range of physical and chemical properties. Cement stabilized specimens produced from these shales were exposed to three different environments. The engineering performance of the stabilized specimens was established through the monitoring of changes in linear dimensions and strength. The sulphur-bearing mineralogy was examined at regular intervals, and the samples were analysed by X-ray diffraction and scanning electron microscopy throughout the study. It is concluded that pyrite, a component of colliery shale, oxidizes in cement stabilized shale. The products of pyrite oxidation may cause distress in the stabilized material through the generation of crystallization pressures or, alternatively, may attack cement hydration minerals. The long-term performance of the stabilized shale is reliably correlated with the original sulphur-bearing mineralogy of the raw shale. Establishment of the limits of total, pyritic and sulphate sulphur are suggested to preclude the use of shales which may cause problems to the long-term durability of cement stabilized colliery shale.