We reported the case of a 63 years old female who presented to the ER with fever, shivering,nausea and lower back pain that appeared four days earlier.She was treated since 2011 for chronic lymphocytic leukemia (with deletion 17p) and hadundergone several therapeutic lines (alemtuzumab, ibrutinib, rituximab-idelalisib). The latterwas stopped 3 months earlier and had been complicated by grade III lymphocytic colitis. Shestarted Venetoclax 2 months before the admission. [...]