A detailed geotechnical and environmental laboratory investigation of phosphogypsum (a by-product of the phosphoric acid production industry) is presented in this paper. The aim of the investigation programme was to evaluate the potential of Greek phosphogypsum for alternative uses, such as in the rehabilitation of quarries and mines by filling voids on or within the ground and as secondary embankment roads. Based on the results, phosphogypsum classifies as low-plasticity silt that is easily compacted at different ranges of moisture content. When compacted, the material develops adequate strength and stiffness. The leachability of most major elements was found to be minimal and the material satisfies common criteria for waste acceptance in landfills. Long-term pilot-scale field tests are necessary in order to evaluate the long-term behaviour of the material in any proposed rehabilitation scheme.