Because adults with acute nonlymphocytic leukemia (ANLL) frequently present with vague complaints and nonspecific finding, it is usually the primary care physician who sees them first. The initial clinical evaluation of such patients should include making the diagnosis, beginning to characterize the leukemia, and assessing the overall medical condition of the patient. All phases of this evaluation should be completed with a sense of urgency because immediate medical intervention is often necessary. Prompt assessment and institution of therapy take on added importance now that effective chemotherapy is available. Currently, a large majority of patients with ANLL respond to treatment and 15% to 20% are probably cured. With the use of various clinical and laboratory studies, the physician can rapidly confirm a suspected diagnosis of ANLL and systematically evaluate the patient's condition prior to arranging for appropriate treatment.