Bladder leiomyosarcoma is a rare mesenchymal tumour, accounting for less than 0.5% of all primary bladder malignancies. Adult women of reproductive age have the higher incidence of bladder leiomyosarcoma. Exposure to local pelvic radiotherapy or systemic chemotherapy, especially cyclophosphamide therapy, is also a significant risk factor. We describe a case of a 31-year-old male who developed urinary bladder leiomyosarcoma. The patient had no history of radiotherapy, systemic chemotherapy, or other significant event, except a 5-year history of ketamine abuse. The tumour was found on the left bladder wall and was definitively diagnosed by transurethral resection of the bladder tumour. A partial cystectomy was performed. There are no known reports of urinary bladder leiomyosarcoma associated with chronic ketamine abuse; therefore, we speculate that chronic ketamine abuse may be a factor in the development of this infrequent bladder malignancy.