We have observed some patients with diabetic macular edema who did not respond to grid laser treatment and who improved with spontaneous posterior vitreous detachment or vitrectomy. These cases have a taut and glistening vitreo-macular interface. Three such cases are presented in detail. Pars plana vitrectomy with separation of the posterior hyaloid was performed in 22 cases. All of them had proliferative diabetic retinopathy, previously treated by panretinal photocoagulation. Fourteen cases had an ineffective macular grid laser treatment. Postoperative visual acuity was improved in 19 eyes and was unchanged in three eyes. The macular edema disappeared in 12 eyes and decreased in 10. Complications included a vitreous hemorrhage in 6 eyes, a paramacular tear in 1 eye, a reghmatogenous retinal detachment in 1 eye and cataract formation in 2 eyes. Vitreous surgery can improve the visual prognosis in cases of diabetic macular edema associated with a pathological vitreo-macular interface.