The protein moiety of lipoprotein (a) consists of apoB-100 and apolipoprotein (a). Lipoprotein (a) is an independent risk factor for premature atherosclerosis. Apolipoprotein (a) and plasminogen are structurally homologous. Through interference with the fibrinolytic system, lipoprotein (a) may act as a thrombogenic factor. In the present study, we determined lipoprotein (a) concentrations in 84 patients (60 men and 24 women) with retinal vascular occlusion (RVO) and in 2 groups of healthy volunteers (n = 40 and 46). In all, 29% of the patients had Lp (a) levels of above 300 mg/l. In the two reference groups, only 10% and 9% of the subjects exceeded this level. According to the chi-square test, the association between Lp (a) levels and RVO was significant. Lp (a) concentrations did not differ between patients with arterial occlusion and those with venous occlusion. No difference in the total cholesterol, triglyceride, or LDL-cholesterol values was observed between patients and controls. We therefore conclude that Lp (a) represents an independent risk factor for RVO.