Ambystoma annulatum has a slender girth, well-rounded body and, among salamanders, a generally small head and long tail. Adults grow to a range of 140-180 mm snout-vent length, with a record length of 255 mm. This species usually has 15 costal grooves (Behler 1996). It has a depressed snout that is evenly and bluntly rounded. Vomerine teeth are arrayed in two short series located entirely behind the choanae. Each series consists of about 7-11 small, blunt teeth. There are five toes on each hind foot (Bishop 1962).
In life, the dorsal color of adults ranges from dark gray to blackish brown, with contrasting white to yellowish bands. Ventrally, the color varies from light gray to yellowish, peppered with light-colored spots. There is typically a short, light colored bar between the eyes that may continue below the eyes to point diagonally posterior. Recently metamorphosed juveniles have a drab green to dark gray dorsal surface, and a row of dorsolateral yellowish spots extending from the front limbs to the tip of the tail. Laterally, a broad band runs from the gills two-thirds of the way down the tail, which lacks pigmentation. Bellies are grayish-yellow. Juveniles develop the blotches or rings that characterize this species approximately two months after metamorphosis (Hutcherson et al. 1998). The sexes are monomorphic and it is unknown whether there is any geographic or seasonal variation (Bishop 1962; Johnson 1977; Petranka 1998).
The specific epithet annulatum means "ringed" (Beltz 2002).