Background & Aims: The percentage of Lens culinaris agglutinin-reactive (α)-fetoprotein (AFP-L3%) is proposed as a diagnostic and prognostic marker for hepatocellular carcinoma (HCC). We evaluated the utility of AFP-L3% for diagnosis of HCC in a US referral population. Methods: This retrospective study included 272 patients: 166 with HCC and 106 with benign liver disease (chronic liver disease, 77; benign liver mass, 29). The AFP-L3% was measured using a clinical auto-analyzer. Results: The AFP-L3% is not reported for a total α-fetoprotein (AFP) less than 10 ng/mL, and all patients with an AFP greater than 200 ng/mL had HCC; thus the AFP-L3% was noninformative for these patients. In patients with a total AFP of 10-200 ng/mL, an AFP-L3% greater than 10% had a sensitivity of 71% and a specificity of 63% for diagnosis of HCC. An AFP-L3% greater than 35% had a reduced sensitivity of 33%, but an increased specificity of 100%. The high specificity of the AFP-L3% cut-off of 35% allowed the confident diagnosis of an additional 10% of HCCs not diagnosed using an AFP cut-off of 200 ng/mL. After adjustment for AFP level, no association was observed between AFP-L3% and tumor size, stage, vascular invasion, grade, or survival. Conclusions: Patients with indeterminate total AFP values of 10-200 ng/mL present a diagnostic dilemma. We found that an AFP-L3% greater than 35% has 100% specificity for HCC in these patients. AFP-L3%, used in combination with AFP, may be a clinically useful adjunct marker for the diagnosis of HCC.