A 28 year-old Italian woman and her husband were found to be carriers of different alleles of β-thalassaemia. Upon presentation of a twin pregnancy prenatal diagnosis was requested. Sampling of foetal material was performed for each placenta by transabdominal CVS, without any complications for the embryos or the mother resulting from this procedure. The material obtained was used to perform a number of molecular biology tests (sequencing, restriction analysis, ARMS, and dot blot) that allowed the determination and confirmation of the genotype of each embryo: one of the foetuses was heterozygous for the maternal allele β39 C->T and the other one was heterozygous for the paternal allele IVS-1 nt 110 G->A. In this paper we discuss the different options for patients carrying an abnormal foetus in the context of a twin pregnancy as well as ethical and legal implications. We show that transabdominal CVS is a safe and reliable way of obtaining foetal material, and that prenatal diagnosis can be performed using a number of different techniques. Although we agree with selective termination of an abnormal foetus in twin pregnancy, we discuss why this attitude will remain controversial, especially in a central european ethico-legal context.