The importance of cellular infiltrates in tissues has been investigated as a diagnostic tool, mechanism of pathogenesis, and prognostic indicator in certain human diseases. Eosinophils, in particular, have a distinct role in the development of cutaneous lesions in human autoimmune diseases. Identification of an eosinophilic infiltrate can aid the diagnosis of immunobullous disease in the early stages of the disease process. In canine pemphigus foliaceus, eosinophils are present to a variable degree within lesional tissue. This study retrospectively evaluated 40 dogs with pemphigus foliaceus, and examined clinical and histologic features and final outcomes in cases with and without eosinophilic infiltrates. Twenty-five of 40 dogs (63%) had an eosinophilic infiltrate in either the pustules/crust, follicular infundibulum or dermis. There was no statistically significant difference in clinical distribution or appearance of dermatological lesions, response to treatment, or disease outcome in dogs with or without an eosinophilic infiltrate. However, dogs with concurrent disease were significantly more likely to have an eosinophilic infiltrate (P = 0.01). Dogs with adverse effects associated with immunosuppressive therapy were significantly more likely to have an eosinophilic infiltrate (P = 0.05). Fifteen of 40 dogs (38%) had a history of allergic disease and a significantly higher proportion of these dogs had an eosinophilic infiltrate (P = 0.04). An eosinophilic infiltrate was found in more than half of the dogs in this study. These findings justify further studies to investigate the role of eosinophils in the pathogenesis, therapy and prognosis in dogs with pemphigus foliaceus.