The cytogenetics, cytology and cytochemistry, clinical findings, therapeutic response and survival of patients presenting with acute leukemia and the Philadelphia chromosome (Ph1) are briefly reviewed based upon a survey of the world literature and 16 cases seen at the University of Minnesota during the last 10 years. Details regarding the 16 cases from the University of Minnesota series are presented and two appendices listing the majority of reports of Ph1 + acute leukemia are included. Comparison of adults with Ph1+ and Ph1- acute leukemia demonstrate important clinical, therapeutic and prognostic differences. In general, patients with Ph1+ acute leukemia respond less well to treatment and survive significantly shorter periods of time. Since the presence of the Philadelphia chromosome in acute leukemia has therapeutic and prognostic significance, marrow chromosome studies should be performed in adults presenting with acute leukemia, especially acute lymphocytic leukemia.