Fabry disease (FD) is a rare X-linked disorder caused by a deficiency of lysosomal α-galactosidase A activity. Treatment with recombinant enzyme replacement therapy is available since 2001 and the effects of anti-drug antibodies (ADA) on therapy efficacy and disease outcome in affected patients have been controversially reported. In this letter we discuss the importance of adequate measurements of neutralizing ADAs and appropriate longitudinal analysis to determine therapy efficiency and clinical outcome in patients with FD.