Patients presenting with fever and rash are one of the common symptom complexes presenting in medical practice. Because of the wide range of diseases that can present with this complex, the patient presenting with fever and rash is also one of the most challenging clinical syndromes.

Although both infectious and noninfectious disease processes can present with fever and rash, infectious causes are considered here. Nevertheless, noninfectious causes such as drug reactions, systemic vasculitis, serum sickness, erythema multiforme, toxic epidermal necrolysis, and Sweet's syndrome are often in the differential diagnosis.

The approach to the patient with infectious fever and rash should begin with the appreciation that causes include common infections that are often benign, serious emergent infections that can be rapidly fatal, and unusual infections that can pose a diagnostic challenge. Key features in the history and physical can be particularly important. These include childhood diseases and immunization history, seasonal diseases, travel history and geography, exposure, sexual history, and medication usage, as well as prodromal and accompanying symptoms. Physical examination, with particular attention to the characteristics of the rash, can be key, along with vital signs to assess severity of the illness, and particular attention to meningeal signs, lymph nodes, mucus membranes, conjunctiva, and joint examination.