Immersion A- and B-scan ultrasonography was performed before vitreous surgery in 256 eyes with diabetic vitreous hemorrhage. Of 32 eyes with vitreous hemorrhage without vitreous traction (group 1), 28 (88%) showed useful postoperative vision. Of 87 eyes with vitreous traction without tractional retinal detachment (group 2), 69 (79%) had useful postoperative vision. Eyes with tractional retinal detachments were classified as follows: X-shaped detachment with narrow vitreoretinal adhesions (group 3, 75 eyes), and H-shaped detachment with broad vitreoretinal adhesions (group 4, 62 eyes). Useful postoperative vision returned in 43 eyes in group 3 (57%) and in only 14 eyes in group 4 (23%), a statistically significant difference. Visual improvement was greater in groups 1 and 2 than in groups 3 and 4. Postoperative functional results were worse when the macular area was the site of vitreoretinal adhesion and traction.