Unlike its devastating teratogenic effects, post-natal infection with rubella typically causes subclinical or inapparent illness. While rubella has been largely eliminated from the United States following the introduction of an efficacious live-attenuated vaccine in 1969, a small proportion of the population remains susceptible. Recent declining vaccination rates have resulted in a rising incidence of sporadic and outbreak-associated measles, reminding us that an increasing proportion of the population is also susceptible to, and may be reservoirs of transmission for, rubella. We describe two rare adult cases with no clear exposure. These cases serve as a reminder that clinicians should remain vigilant and consider rubella infection in susceptible patients, including older adults, presenting with febrile rash illness.