Technological and other advances over the past decades have led to the discovery of thousands of gene-disease associations for autosomal and X-linked recessive Mendelian disorders. Combined with recent improvements in assessing individual variants in each human genome, these developments offer the possibility of testing populations for all known severe recessive genetic disorders. Past experience has provided the framework for expanded carrier screening, but many challenges remain regarding which disorders to include, how to interpret variants and how to incorporate newly discovered gene-disease links into existing screening programmes.