Familial combined hyperlipidemia (FCHL) is one of the most common inherited lipid disorders. Resistance of adipocytes to the effects of acylation stimulating protein (ASP) may contribute to ineffective triglyceride synthesis and thereby prolonged postprandial lipemia and increased fatty acid flux to the liver seen in FCHL patients. Interestingly, ASP is identical to C3a-desArg, fragment of the third component of complement. We examined the relationships between serum levels of complement components C3 and C4 and markers of lipid and glucose metabolism in 11 large FCHL families (n = 53). Median serum C3 levels were 38% higher in affected compared to non-affected male FCHL family members (1.90 g/l vs. 1.38, P = 0.0027). The strongest correlations were observed between serum complement C3 and apolipoprotein B levels, reaching 0.77 in males. These relations were not confounded by obesity or impaired glucose tolerance. In conclusion, serum levels of the main complement components C3 and C4 correlated significantly with serum lipid levels. Further studies are needed to clarify the importance of disturbances in the complement system on the pathogenesis of FCHL and other lipid disorders.