Familial combined hyperlipidemia (FCHL) is a dyslipidemic syndrome prevalent in patients with coronary artery disease. Other phenotypes that appear to have a kinship with FCHL include hyperapobetalipoproteinemia, LDL subclass pattern B, familial dyslipidemic hypertension, and syndrome X. The metabolic, genetic, and molecular basis of FCHL is heterogeneous. This review discusses the influence of eight putative loci as a basis for this heterogeneity. Further understanding of the fundamental defects underlying FCHL and related syndromes may provide important insights into the pathophysiology of coronary artery disease.