Purpose: To evaluate the retrobulbar hemodynamics in eyes with optic neuritis with multiple sclerosis and to compare these values with those of the unaffected fellow eyes and healthy control eyes. Methods: Thirty-four eyes of 17 patients with unilateral optic neuritis and multiple sclerosis and 16 eyes of 16 normal healthy subjects were recruited from the Departments of Ophthalmology and Neurology. The peak systolic and end-diastolic blood flow velocities and resistivity indices of the ophthalmic artery, posterior ciliary arteries and central retinal artery were measured in each eye with optic neuritis, using color Doppler imaging. Then, they were compared with those of the unaffected fellow eyes and healthy control eyes using paired and unpaired Student's t-tests, respectively. Results: The mean etrobulbar blood flow velocities and mean resistivity index in the ophthalmic artery in the eyes with optic neuritis were not significantly different from the unaffected fellow eyes and healthy control eyes, as well (P>0.05). The mean end-diastolic blood flow velocity in the central retinal artery (P=0.04) was lower and mean resistivity indices in the central retinal (P=0.02) and posterior ciliary arteries (P=0.009) were higher in the eyes with optic neuritis than in the control eyes. In patients with multiple sclerosis, the eyes with optic neuritis had higher resistivity indices in the posterior ciliary (P=0.02) and central retinal arteries (P=0.04) than did the unaffected fellow eyes. The retrobulbar blood flow velocities and resistivity indices of all vessels in the unaffected fellow eyes did not significantly differ from the control eyes (P>0.05). Conclusions: This study suggests that optic neuritis with multiple sclerosis is associated with impaired retrobulbar hemodynamics, especially in the posterior ciliary and central retinal arteries when compared with the contralateral unaffected eyes as well as healthy control eyes. © Springer-Verlag 2004.