A 10-week-old female infant presented with a right-sided facial swelling without any constitutional symptoms. The swelling was nontender, nonfluctuant, with no erythema or induration. On the basis of the clinical picture, magnetic resonance imaging findings and serology, a diagnosis of unilateral mumps parotitis was made. The United Kingdom is currently experiencing a mumps epidemic with a 28-fold rise in the number of cases over the last 10 years. Infants are being increasingly affected. Mumps parotitis, which was previously unreported in infants, needs to be considered as part of the differential diagnosis when a small child presents with swelling of the parotid gland.