During a mumps outbreak, the diagnosis is made easily in patients with parotitis and a history of recent exposure; however, when disease incidence is low, other causes of parotitis should be considered and laboratory testing is required for case confirmation. Infectious causes of parotitis include other viruses (e.g., HIV, coxsackievirus, parainfluenza virus type 3, influenza A virus, Epstein-Barr virus, adenovirus, parvovirus B19, lymphocytic choriomeningitis virus, human herpesvirus 6), gram-positive bacteria, atypical mycobacteria, and Bartonella species. Rarely, other gram-negative or anaerobic bacteria are associated with parotitis. Parotitis can also develop in the setting of sarcoidosis, Sjögren’s syndrome, Mikulicz’s syndrome, Parinaud’s syndrome, uremia, diabetes mellitus, laundry starch ingestion, malnutrition, cirrhosis, and some drug treatments. Unilateral parotitis can be caused by ductal obstruction, cysts, and tumors. In the absence of parotitis or other salivary gland enlargement, symptoms of other visceral organ and/or CNS involvement may predominate, and a laboratory diagnosis is required. Other entities should be considered when manifestations consistent with mumps appear in organs other than the parotid. Testicular torsion may produce a painful scrotal mass resembling that seen in mumps orchitis. Other viruses (e.g., enteroviruses) may cause aseptic meningitis that is clinically indistinguishable from that due to mumps virus.