The spotted salamander is a relatively large member of the family Ambystomatidae. Adults reach 15-25 cm total length, and have 11-13 costal grooves. Adult spotted salamanders typically contain two irregular rows of yellowish spots on a black to dark gray dorsum, though some populations contain low frequencies of individuals lacking any spotting in addition to albinos or partial albinos. Certain populations exhibit bright orange markings on the head, a pattern that has not been correlated with any taxonomic divisions. During the breeding season males have very conspicuously swollen vents, and females in breeding condition are typically larger than males. Hatchlings of this species do not contain readily identifiable markings and are characterized simply by a dull olive green color. Hatchlings may measure 12-17 mm in total length (Petranka 1998).
The taxonomy for the species remains stable though some researchers point out distinct mitochondrial clades. Phillips (1994) identified two divergent, geographically separate lineages in the Ozarks region differing by a minimum of 19 mitochondrial DNA restriction sites.