Detrusor-sphincter dyssynergia (DSD) is a condition in which the urethral outlet actively contracts during a detrusor contraction. This is most often caused by isolated and complete suprasacral spinal cord lesions and can be manifested by external urethral sphincter (EUS) or bladder neck/ proximal urethral smooth muscle contraction, or both, reflexly generated against a hyperreflexive detrusor contraction. The resultant generation of high intravesical pressures, if left untreated, can cause damage to the bladder itself and result in ureteral reflux, hydronephrosis, and renal failure. Current therapies solve some problems but do not address the underlying pathology. Thus, understanding the pathophysiology underlying EUS DSD remains a priority in the urologic care of patients with suprasacral transverse spinal myelopathies. This review examines data and concepts from animals and humans to elucidate the pathophysiology of EUS DSD.