To assess the correlation between persistent diabetic macular edema and hemoglobin A1c (HbA1C). Retrospective study. Records of type 2 diabetic patients who received eye care for persistent clinically significant macular edema (CSME) from January 2002 to January 2004 were reviewed. Subjects who met one of two criteria were identified: 1) persistent CSME, detected by contact lens biomicroscopy and fluorescein angiography, despite at least two focal laser photocoagulations (FLP) performed at least 3 months before the current diagnosis, or 2) a history of CSME with resolution of macular edema at the time of examination. Patients also needed to have had their HbA1C measured at the Johns Hopkins Hospitals within 3 months of meeting these criteria. The study identified 92 patients (152) eyes with persistent CSME and 32 patients (56 eyes) with resolved CSME. HbA1C values ranged from 5.3% to 15.6% (mean, 8.9%; median, 8.7%) and 5.3% to 9.7% (mean, 6.7%; median, 6.6%) among patients with persistent and resolved edema (P = .0005). Among the 32 patients with persistent unilateral CSME, mean HbA1C was 8.6% (median 8.5%), and among the 60 patients with bilateral CSME, mean HbA1C was 9.1% (median, 8.9%). Of patients with persistent CSME, 74% had HbA1C greater than 7.5% compared with 12.5% of the patients with resolved CSME (P = .0005). Persons with type 2 diabetes and persistent CSME have higher HbA1C at time of their disease than patients with resolved CSME. Patients with bilateral disease have more elevated HbA1C than those with unilateral disease.