The authors review the classic course of common pediatric diseases associated with rashes, including varicella-zoster virus, herpes simplex virus (HSV), roseola, and rubella. Understanding the classic patterns, disease progression, high-risk populations, and potential complications allow the ED physician to avoid unnecessary testing in low-risk patients with a classic presentation, and aggressively approach potentially significant rashes in high-risk populations (e.g., neonatal HSV).