The present study retrospectively analyzed clinicopathological and clinical data from 43 adult patients with biphenotypic acute leukemia (BAL) from 11 Korean institutes. The incidence of BAL was 2.1% among acute leukemias. In terms of immunophenotype, 31 patients had myeloid plus B-lymphoid (M + B), 10 had myeloid plus T-lymphoid (M + T), one had myeloid plus B-lymphoid plus T-lymphoid (M + B + T), and one had B-lymphoid plus T-lymphoid (B + T). Patients with M + T phenotype had significantly lower CR rate (55.6% vs. 88.0%, P = 0.039) and lower overall survival (0% vs. 33.9% at 5 years, P = 0.028) than those with M + B phenotype. Our results suggest that immunophenotype has prognostic implications in adult patients with BAL.