Equine gammaherpesviruses are commonly found in healthy horses worldwide. Although most horses are asymptomatic, equine herpesvirus 2 (EHV2) has been associated with granulomatous nodular dermatitis in one horse and EHV5 has been associated with equine multinodular pulmonary fibrosis (EMPF) and interface dermatitis on the face of horses. Equine sarcoidosis is a granulomatous skin condition of horses that can cause exfoliative dermatitis and nodular skin disease, but currently, the underlying cause of equine sarcoidosis is unknown. Because gammaherpesviruses have been associated with granulomatous inflammation, and because the cause of sarcoidosis is unknown, in this study we aim to investigate a potential association between equine gammaherpesvirus and cutaneous sarcoidosis. Our plan is to identify approximately 30 cases of equine cutaneous sarcoidosis from our pathology archives. We will use formalin-fixed paraffin-embedded tissue, extract DNA, and test for EHV2/5 using polymerase chain reaction (PCR). Because DNA extraction from formalin-fixed tissue can be difficult, we will also perform in situ hybridization (ISH) for EHV2/5 through our local diagnostic center. Because fungal infections and mycobacteria species have been associated with granulomatous skin disease in horses, we will also perform special histochemical stains on each case including Gram (for bacteria), Gomori methenamine silver (for fungi) and Ziehl Neelsen (for acid-fast bacteria).