ABSTRACT. Maxillary bone epithelial cyst is rare in dogs. A 5-year-old, spayed female miniature schnauzer developed a swelling below the nasal canthus of left eye. Plain radiograph demonstrated a 1.5 cm diameter of radiolucent lesion on the maxillary bone anteroventral to the eye, and contrast dacryocystorhinography confirmed an obstructed nasolarcrimal duct. The swelling showed poor response to antibiotic treatment but responded well to oral prednisolone. Exploratory surgery revealed a cyst-like structure filled with brown serous fluid. Histopathological examination of the removed cyst revealed a double cuboidal epithelial cyst. The dog recovered rapidly after surgery, and the swelling had not recurred for a 36-month follow-up. It is the first case of periorbital bone epithelial cyst reported in an adult miniature schnauzer. KEY WORDS: bone epithelial cyst, miniature Schnauzer, periorbital swelling.J. Vet. Med. Sci. 70(9): 1001-1004, 2008 The periorbital swelling ventromedial to medial canthus is uncommon in the dog except for periorbital abscess or nasolacrimal diseases. The swelling in the dog may be associated with dacryocystitis [11], nasolacrimal duct obstruction and dilatation, or nasolacrimal neoplasm [7,12] The signalment and history of the patients are essential for deciding a correct direction of diagnosis approach. For example, the age of the patients is helpful to differentiate the likely causes of congenital abnormalities or neoplasm. The active outdoor dogs are prone to injury and traumatic abscess. Imaging examinations including regional radiograph, dacryocystorhinography and ultrasonography can detect anatomical abnormalities. Fine needle aspiration for cytology can confirm the contents of the cyst or cells of the mass.The purpose of this paper was to describe the unique characteristics of an uncommon bone epithelial cyst in an adult miniature schnauzer.Case history: A 5-year-old miniature schnauzer was referred to the ophthalmology clinic at the National Taiwan University Veterinary Hospital (NTUVH) because of a recurred swelling ventromedial to the left eye for 2 months. The swelling had been aspirated and surgically drained twice by local clinics, but the swelling relapsed a few days after surgery. No obvious improvement of the swelling was noted after medical treatment at local clinics.Clinical examinations: The general health condition of the dog was good. Clinical examination revealed a firm swelling (1.5 cm in diameter) attached tightly beneath the left orbital bone, and no oral fistula was found during oral exploration. The pupillary light reflex (PLR) and menace of both eyes were normal. No other ocular abnormalities were found by slit-lamp biomicroscope and indirect ophthalmoscope. Fluorescein passage test showed no intact tear drainage through the left nasolacrimal duct. Cytology of the aspirated seromucoid fluid of the cyst revealed predominant macrophages and several neutrophils, without neoplastic cells. Bacterial and fungal cultures of the serous fluid were negative. Blood examina...