A 77‐year‐old woman with a long term urinary catheter on haemodialysis complained of suprapubic discomfort. The urinary bag was purple (Figure). Urine investigations showed pyuria, and culture grew multiple organisms. Purple urine bag syndrome was diagnosed. This syndrome is rarely reported in dialysis populations.1 Deaminated dietary tryptophan is conjugated to indoxyl sulfate by the liver, then excreted in urine where bacterial sulfatase and phosphatase metabolise it to produce indigo (blue) and indirubin (red) pigments, staining the urinary bag purple.2 Risk factors include chronic catherisation, constipation, urinary tract infection and renal failure.2 Our patient was treated successfully by appropriate antibiotics and catheter replacement.