Dengue and yellow fever are common arboviral infections in humans. The two infections overlap substantially in their epidemiology, pathogenesis, and clinical features. Both infections remain high on the differential diagnosis for any acutely ill patient who has travelled to or lives in an endemic area. Understanding the epidemiology, pathogenesis, and clinical manifestations, together with keeping a high index of suspicion for these infections in the appropriate context, allows for a prompt diagnosis and development of a treatment plan. Patients with yellow fever or dengue typically have active viral replication if they are febrile, allowing for diagnostic confirmation using polymerase chain reaction-based assays, antigen detection assays, or viral culture. Once the period of viremia has passed, diagnosis is supported (usually retrospectively) with serologic assays designed to detect pathogen-specific immunoglobulin (Ig) M, IgG, or neutralizing antibodies. There are no licensed antiviral medications for the treatment of either yellow fever or dengue; the mainstay of therapy is supportive care. The yellow fever 17D vaccine is one of the most successful vaccines of all time and remains widely used in endemic areas of the world. It is also an important travel vaccine. Some countries require proof of vaccination before allowing visitors to enter. Two dengue vaccines have recently been licensed for use, and a third vaccine is on phase III trials, but the vaccines are imperfect leading one manufacturer to cease production. With proper recognition and treatment, the prognosis for patients with dengue is favorable, while the prognosis for patients infected with yellow fever virus remains guarded.