We performed a case-control study to investigate the determinants of macular oedema in patients with diabetes mellitus. Patients with macular oedema (n = 20) were selected for study, together with a random sample of subjects without macular oedema (controls, n = 21). Both groups were similar for sex, type of diabetes, treatment and glycaemic control. Patients with maculopathy had higher systolic and diastolic blood pressure than controls (P < 0.006 and P < 0.03, respectively). Impaired renal function was proportionally higher in patients with maculopathy than in controls (60% vs 47%). Vibratory perception was more impaired in the maculopathy group than the control group (P < 0.02), and maculopathy was associated with the presence of cardiovascular autonomic neuropathy. R-R variation and the brake index were significantly lower in patients than control subjects (P < 0.01 for both). Moreover, the group with maculopathy had a greater fall in systolic blood pressure after standing than did the control group (P < 0.0001). Autonomic neuropathy may be associated with the development of maculopathy and retinopathy, although additional evidence is required to confirm this association. Conditions associated with high blood pressure may accelerate progression and aggravate maculopathy.