Childhood vaccines are a routine part of pediatric care in the United States; clinicians must be able to recognize and interpret associated localized adverse reactions. Redness and induration at the site of injection are commonly reported and are considered to be the result of local inflammation or hematoma formation, although other atypical reactions can occur. We report the case of a 6-month-old infant who developed subcutaneous nodules at the sites of his 4- and 6-month Pentacel (DTaP/Hib/IPV, diphtheria, tetanus, acellular pertussis, Haemophilus b conjugate, and inactivated poliovirus vaccine) and 6-month Prevnar (heptavalent pneumococcal vaccine) injections. Infectious disease and immunodeficiency examinations were unremarkable. Aluminum contact allergy was considered, and contact allergy testing confirmed sensitivity to aluminum. Although rare, aluminum contact allergy after routine immunization can occur and should be considered in the differential diagnosis of persistent subcutaneous nodules after vaccination.