IN this issue of the Journal we begin a new series, "Clinical Problem-Solving," which focuses on the difficult diagnostic, therapeutic, and ethical challenges that physicians face every day. Each installment will consist of a description of a clinical problem encountered in an actual patient, a lightly edited transcript of an impromptu discussion of the clinical situation by an invited clinician, and an illuminating commentary on the problem. The focus on a single patient is intentional; even though we must rely on extensive data from clinical studies to guide our diagnostic and therapeutic practices, we also learn a great deal about . . .