Among 100 patients with acute lymphoblastic leukemia (ALL), 15 B-ALL patients were found positive for surface Her2/neu expression. The incidence in children was only 3.4% compared to 31% in adults (p=0.001). Considering only adult B-ALL patients (n=38), surface Her2/neu expression was associated with chemoresistance (50% versus 11%, p=0.03) suggesting that it could be a prognostic marker of poor clinical outcome in ALL.