Actinomycosis of the urinary bladder is a rare anaerobic bacterial infection caused by Actinomyces isrealii. Initial diagnosis is often difficult and this disease is easily misdiagnosed as a urothelial or urachal tumour. The definitive diagnosis is usually made postoperatively via tissue pathology. We discuss a case of a 54-year-old male with a smoking history and a 2.5-week history of gross hematuria. Ultrasound, computed tomography and cystoscopy revealed a large inflammatory mass adherent to the right, anterior bladder wall, suggesting malignancy. Transurethral resection and histological pathology subsequently confirmed inflammatory urothelium and gram-positive bacteria consistent with actinomyces species.