Detrusor-sphincter dyssynergia is an involuntary contraction of the external urethral sphincter during the detrusor contraction. It causes voiding dysfunction and can lead to urologic complications such as hydroureteronephrosis and renal failure. Patients with spinal cord injuries are particularly vulnerable. Botulinum toxin has been used via cystoscopy to decrease the activity of the external urethral sphincter. This report describes the treatment of 5 tetraplegic patients by single transperineal injections of botulinum toxin for detrusor-sphincter dyssynergia, proved by a urodynamic study with electromyography. A total of 15 injections was given, resulting in improved bladder function in all patients. Urodynamic assessment after treatment showed an increase of the functional detrusor capacity and a decrease of the maximal detrusor pressure during voiding. These results confirm the consideration of botulinum toxin as a treatment for detrusor sphincter dyssynergia. A single transperineal injection is a valuable, less invasive treatment using a cystoscopic technique.