We measured the breakdown of the blood-aqueous barrier in 63 patients with diabetes (126 eyes) by using a laser flare meter. Of 126 eyes, 40 had no retinopathy, 34 had proliferative retinopathy, 24 had regressed proliferative retinopathy, 14 had background retinopathy, and 14 had maculopathy. Eyes were classified into one category only. Mean flare was greater for proliferative retinopathy compared to background retinopathy (P = .0065), no retinopathy (P = .0001), and maculopathy (P = .0189). Flare values were greater for regressed proliferative retinopathy compared to no retinopathy (P = .0118) (paired Student's t-test). Diabetic eyes without demonstrable retinopathy still had higher flare values than control eyes without diabetes. The length of diabetes was greater for those eyes with proliferative diabetic retinopathy (P = .0195), regressed proliferative diabetic retinopathy (P = .0625), and background diabetic retinopathy (P = .006) compared to those with no retinopathy. No significant difference was noted in duration of diabetes for eyes with diabetic maculopathy when compared to those with no retinopathy (P = .5788). Breakdown of the blood-aqueous barrier precedes the development of retinopathy, and the more severe proliferative forms have greater blood-aqueous barrier dysfunction.