OBJECTIVE: To examine the relationship of retinal vascular caliber to macular telangiectasia (MT) type 2. DESIGN: Case-control study. PARTICIPANTS: Patients with MT aged 18 years and older were identified from Australian sites of the multicenter Macular Telangiectasia Project. Three controls per case were selected from participants of the Australian Diabetes, Obesity and Lifestyle study, matched according to age and diabetes status. METHODS: Baseline ophthalmic examinations of cases included assessment of best corrected visual acuity, fluorescein angiography, autofluorescence imaging, optical coherence tomography, and retinal photography. Retinal vascular caliber of cases and controls were measured from optic disc-centered digital retinal images by a computer-assisted method. MAIN OUTCOME MEASURES: MT, central retinal arteriolar, and venular caliber. RESULTS: There were 55 cases and 170 controls. After controlling for diastolic blood pressure, total cholesterol, high-density lipoprotein cholesterol, triglycerides, hypertension, fasting plasma glucose, and glycosylated hemoglobin, each standard deviation (SD) increase in retinal arteriolar caliber was associated with a 2-fold higher odds of MT (odds ratio [OR] 2.18; 95% confidence interval [CI], 1.50-3.18). Similarly, each SD increase in retinal venular caliber was associated with increased odds of having MT (OR 1.87; 95% CI, 1.31-2.67). CONCLUSIONS: This study shows that MT is associated with wider arteriolar and venular caliber, measured outside of the foveal area. Generalized changes in retinal vascular caliber may reflect underlying dysfunction in retinal pericytes or glial cells, and may provide a means to monitor progression of disease. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found after the references.