"Paranthodon" was a small relative of larger stegosaurids such as "Stegosaurus". Thomas R. Holtz Jr. estimated that the animal was long and weighed between . The snout is elongated, though not extremely so, and on top. The back of the premaxilla is long and broad, and the external nares are large. The teeth have a prominent primary ridge. The fossilised nasal and maxillary bones are relatively complete, and an incomplete premaxilla is also preserved. The partial snout resembles "Stegosaurus" in its large posterior premaxillary process and the extension of the palate. "Stegosaurus" was the only stegosaurid known from adequate cranial material to compare with "Paranthodon" during the 1981 review of the taxon, and even though their resemblance is great, tooth morphology is very distinguishing among the stegosaurians. For example, cranial material is known from "Stegosaurus", "Paranthodon", "Kentrosaurus", and "Tuojiangosaurus", and the tooth morphology differs in all of them.