Barbara Eichhorst, MD, from the University of Cologne, Cologne, Germany, discusses implications of genetic testing in chronic lymphocytic leukemia (CLL) at the 2017 British Society for Haematology (BSH) Annual Scientific Meeting in Brighton, UK. She describes different techniques used for genetic analysis, including FISH, Sanger sequencing and next-generation sequencing (NGS), and discusses thresholds for the proportion of CLL cells expressing particular markers and what this means for treatment. Dr Eichhorst also highlights that this examination should be done before every treatment decision.