Urinary symptoms occur in 19% of human T-cell lymphotropic virus type 1 (HTLV-1)-infected patients who do not fulfi ll criteria for HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and in almost 100% of HAM/TSP patients. Few studies have evaluated therapies for overactive bladder (OAB) caused by HTLV-1 infection. This case report describes the effect of onabotulinum toxin A on the urinary manifestations of three patients with HAM/TSP and OAB symptoms. The patients were intravesically administered 200 units of Botox®. Their incontinence episodes improved, and their OAB symptoms scores (OABSS) reduced signifi cantly. These data indicate that Botox® should be a treatment option for OAB associated with HTLV-1 infection.