Eczema vaccinatum (EV) is a complication of smallpox vaccination occurring in patients with atopic dermatitis. In affected individuals, vaccinia virus (VV) spreads through the skin, resulting in large primary lesions and satellite lesions, and infects internal organs. BALB/c mice inoculated with VV at sites of Th2-biased allergic skin inflammation elicited by epicutaneous ovalbumin (OVA) sensitization exhibited larger primary lesions that were erosive, more satellite lesions, and higher viral loads in skin and internal organs than mice inoculated in saline-exposed skin, unsensitized skin, or skin sites with Th1-dominant inflammation. VV inoculation in OVA-sensitized skin induced marked local expression of IL-17 transcripts and massive neutrophil infiltration compared to VV inoculation in saline-exposed skin. Treatment with anti-IL-17 decreased the size of primary lesions, numbers of satellite lesions, and viral loads. Addition of IL-17 promoted VV replication in skin explants. These results suggest that IL-17 may be a potential therapeutic target in EV.