UNLABELLED: This case report details haemorrhagic cystitis in a 49-year-old female with chronic lymphocytic leukaemia (CLL), recurrent haematuria and detected BK polyomavirus (BKPyV) and adenovirus (HAdV) in urine. During chemotherapy cycles, quantitative polymerase chain reaction (PCR) assays found high HAdV load, similar to a HAdV-B2 genotype 78, a rare genotype that is closely related to HAdV-11. CONTRIBUTION: Viral interactions reveal immune system vulnerabilities.