Between July 1992 and July 2001, 81 patients with de novo adult acute lymphoblastic leukemia (ALL) treated according to the German Multicenter Study Group for Adult ALL (GMALL) 01/81 protocol were evaluated in order to analyze the effect of aberrant myeloid antigen expression on prognosis. We observed myeloid antigen aberrant expression in 21 of the adult ALL cases. We did not observe any effect of aberrant myeloid antigen expression on the time to achieve remission, relapse rate, and death rate. After 5 years of follow-up, cumulative disease-free survival of myeloid antigen (My) (+) and My (-) adult ALL patients was 67% and 43%, respectively. These data were not found to be statistically significant (P=0.29), but we did find a statistically significant difference in overall survivals between these two groups (85% vs 50%) (P=0.05). Twenty-nine patients died and the remaining 52 patients were followed for a median of 31 months. We could not find any special effect of the known prognostic factors on prediction of relapse in multivariate analysis. However, myeloid antigen expression was the most significant factor, which affected long-term survival in our patients (P=0.01). These data indicate that myeloid antigen expression is useful for predicting a favorable outcome of adult patients with ALL.