AIMS: To investigate whether lupus anticoagulant (LA) positivity, a marker of endothelial dysfunction, might be relevant to the pathogenesis of diabetic retinopathy (DR). METHODS: 32 IDDM patients were examined for LA, fibrinogen, prothrombin (PT), PTT, prothrombin degradation products (F1+2), and activated protein C (APC). RESULTS: APC decreased and F1+2 increased significantly in LA positive but not in LA negative patients; 60% of LA positive and 18% of LA negative subjects had DR. PT, PTT, and fibrinogen levels were insignificant. CONCLUSION: These preliminary findings suggest that LA positivity could represent an additional risk factor for DR, acting as a link between the immunological and haemostatic systems.