Acute rhinosinusitis is a common ailment accounting for millions of office visits annually, including that of Mrs D, a 51-year-old woman presenting with 5 days of upper respiratory illness and facial pain. Her case is used to review the diagnosis and treatment of acute rhinosinusitis. Acute viral rhinosinusitis can be difficult to distinguish from acute bacterial rhinosinusitis, especially during the first 10 days of symptoms. Evidence-based clinical practice guidelines developed to guide diagnosis and treatment of acute viral and bacterial rhinosinusitis recommend that the diagnosis of acute rhinosinusitis be based on the presence of "cardinal symptoms" of purulent rhinorrhea and either facial pressure or nasal obstruction of less than 4 weeks' duration. Antibiotic treatment generally can be withheld during the first 10 days of symptoms for mild to moderate cases, given the likelihood of acute viral rhinosinusitis or of spontaneously resolving acute bacterial rhinosinusitis. After 10 days, the likelihood of acute bacterial rhinosinusitis increases, and initiation of antibiotic therapy is supported by practice guidelines. Complications of sinusitis, though rare, can be serious and require early recognition and treatment.