Abstract
The symptom of macroscopic or 'visible' haematuria can cause significant patient distress, largely due to its' potential association with urinary tract malignancy, infection or glomerular disease. This lesson from practice describes the case of a 19-year-old female patient for whom the cause of red/brown urinary discolouration was found to relate to a reaction between renally excreted mesalazine and domestic bleach in the toilet bowel. Recognition of this phenomenon in patients taking mesalazine for inflammatory colitis is important to minimise patient distress and unnecessary investigation for a urinary tract cause.