Physicians are trained to assume that a simple single diagnosis is typically the most sound. In evaluating patients with an altered mental status, they usually use the history, physical examination, and laboratory results to arrive at a single reasonable etiology that explains the presenting symptoms. However, this process involves the risk that some of the symptoms will create certainty about a single diagnosis and bring premature closure to the workup, when the patient actually has multiple diagnoses which contribute to the altered mental status. In this article, the authors describe the case of a patient who presents with altered mental status. Attempting to locate a single, unifying diagnosis led the patient's physicians away from diagnosing the multiple disorders that were actually present in this one patient. It was the role of the consulting psychiatrist to augment the diagnostic process and enable the primary care physician to consider multiple diagnostic etiologies. In this patient, as in many patients who have complex presentations, the underlying etiology is substance abuse. The physician's countertransference to patients with substance abuse may contribute to the premature closure of the diagnostic process.