Infusion of ex vivo transduced haematopoietic stem cells (HSC) has emerged as a promising new treatment of certain monogenetic disorders. Since early clinical studies on patients with severe combined immune deficiency were halted due to de novo leukaemia, the technology has matured. Thus, treatment of transfusion-dependent thalassaemia and adenosine deaminase deficient severe combined immunodeficiency by using lentiviral vectors for gene correction of autologous HSC can induce expression of the deficient protein and thus potentially cure the patients. The review summarises recent advances allowing for clinical implementation of the treatment in Denmark.