Parafoveal telangiectasia is a microvascular abnormality of the macula that may be developmental or acquired. Twenty-eight patients with this condition and normal fasting blood glucose levels underwent ophthalmologic evaluation and glucose tolerance testing. Bilateral telangiectasia was more frequently associated with laboratory evidence of abnormal glucose metabolism than unilateral disease (five of eight cases vs six of 17 cases). In five of our patients, results of glucose tolerance testing were consistent with diabetes even though fasting blood glucose levels were normal. Right-angle venules, which have been reported to be an important sign of bilateral disease, were also found in unilateral telangiectasia. Unilateral telangiectasia occurs in females as well as males. Glucose tolerance testing should be performed in all patients who have bilateral parafoveal telangiectasia.