Reduced fertility in men with spinal cord injury results from the inability to ejaculate and poor semen quality. Vibratory penile stimulation can induce ejaculation in many men with spinal cord injuries, but few studies have reported the effects of repeated vibratory stimulation on quantitative semen analysis tests. Fourteen spinal cord-injured males were enrolled in a prospective study to develop a quantitative profile of antegrade and retrograde ejaculate specimens collected during repeated vibratory stimulation. Antegrade specimens were obtained in 51 (84%) and retrograde specimens were obtained in all of the 61 trials (100%). Sperm were present in 70% and 64% of the antegrade and retrograde samples, respectively. Of the patients who underwent repeated vibratory stimulation attempts, three showed marked improvement in sperm counts and characteristics with repeated vibration and five showed normal fluctuation or no change in semen quality. Overall, there was a trend toward higher sperm counts in the antegrade samples (mean, 74.1 million) than in the retrograde samples (mean, 40 million), but no statistical significance was found. Mean sperm motility, sperm progressive motility, and percent normal sperm morphology were not significantly different between antegrade and retrograde specimens. Fructose and zinc, semen markers that reflect the presence of a true ejaculate, were present in all antegrade and retrograde specimens. In conclusion, (1) both antegrade and retrograde ejaculation occur with vibratory penile stimulation, with antegrade samples containing greater numbers of sperm but retrograde samples also having significant sperm counts, (2) repeated vibration may increase sperm concentration or may result in only minimal changes reflective of normal fluctuations, and (3) vibratory stimulation results in true ejaculation, as evidenced by semen markers.