This prospective study aimed at determining whether nocturnal penile tumescence and rigidity (NPTR) findings correlate to the neurologic disorders in spinal cord injured (SCI) patients suffering from erectile dysfunction (ED). A total of 25 acute SCI male patients with post-traumatic ED underwent neurological, electrophysiological and urodynamic examinations, respectively, as well as NPTR recordings. The mean value for rigidity (R), tumescence (T) and duration (D) during NTPR tests were 83.3%, 3.3 cm, 6.4 min in patients with a complete lesion above the sacral (S2-S4) spinal cord (n=10), 46.1%, 1.6 cm, 5.5 min in patients with a complete lesion involving the sacral metameres (n=5) and 89.8%, 3.8 cm, 29 min in patients with an incomplete suprasacral lesion (n=7). The differences among these groups were statistically significant (P<0.05). Patients with lesions involving both sacral and thoracolumbar spinal cord showed no erections (n=3). We found four NTPR patterns: (1) normal R and T, short D; (2) weak R and T, short D; (3) normal R, T and D; and (4) no erections, which can be assigned to different levels and completeness of spinal cord lesions. Nocturnal erections of normal quality need preservation of thoracolumbar and sacral neuronal control as well as partially intact connections of the spinal erection centres with brain areas responsible for sexual arousal.