CDC helped state officials investigate a mumps outbreak that spread to about 300 University of Iowa students between July 2015 and May 2016. The vast majority of affected students—including 20 who experienced complications—had received at least 2 doses of MMR vaccine. Considering the limited existing data on presentation and clinical course of complications in mumps patients who were vaccinated as recommended, CDC put together a case series involving orchitis, transient hearing loss, and meningitis. In the orchitis case, a male student developed testicular pain and swelling on day 9, even though parotitis was no longer present. The condition was treated with NSAIDs and ice packs, with no additional followup care required. A female student received a probable mumps diagnosis when her symptoms—progressive right ear pain, cough, and shortness of breath—worsened after emergency department personnel prescribed her amoxicillin and analgesics for what they determined to be otitis. She noticed tinnitus and diminished hearing in one ear 3 days after her symptoms began; and audiology testing on day 8 confirmed right sensorineural hearing loss due to mumps and conductive hearing loss due to otitis media and myringitis. After 1 week on prednisone, the patient's symptoms resolved. Finally, another male patient sought emergency care for neck stiffness, fever, and tachycardia 22 days after caregivers attributed his initial symptoms of facial pain and swelling to mumps. It was determined that he likely had mumps-associated viral meningitis, which can present anywhere from 4 days before to 3 weeks after the onset of parotitis. The case studies underscore that complications occur even within vaccinated populations and can present at varying times throughout the course of illness and even when parotitis has ended.