Secondary glaucomas are common in dogs, and occur due to obstruction of aqueous humor flow at the pupil, iridocorneal angle, or trabecular meshwork by numerous mechanisms. Secondary glaucoma is suspected based on examination findings, or presence of elevated IOP in an animal with a signalment inconsistent with primary glaucoma. Animals with secondary glaucoma require more diagnostic testing than animals with primary glaucoma. Management is challenging, and treatments used for primary glaucoma may be ineffective or even detrimental. Prognosis for vision and/or globe retention may be better than for primary glaucoma, particularly if underlying causes can be found and addressed promptly.