Waste gypsum from the construction materials sector is an important part of the construction and demolition waste (CDW). Although pure gypsum can be recycled infinitely, impure waste gypsum is often disposed of or dispersed in the CDW stream. Source separation is not performed on a large scale and sorting units for CDW often do not perform a gypsum selection. The sulphate content is a major criterion in the valorisation of the CDW as a secondary aggregate for concrete. Therefore, the question arises whether the presence of residual gypsum in CDW masonry aggregates is a burden for effective valorisation. The actual gypsum content and sulphate leachability was studied for a range of sorted and recycled aggregates. This was compared to the overall environmental quality of the material. Visual analysis of the various products from sorting and recycling gave data on the gypsum content. On this basis a material flow diagram of gypsum is set up. This allows to determine the gypsum recycling potential on the Flemish market. In order to optimise gypsum recycling from CDW, source selection measures need to be taken and a centralised collection and treatment system needs to be set up.