The type species, S. osborni, was described by Barnum Brown in 1912. The other valid species, S. angustirostris, lived in Asia, and was described by Anatoly Konstantinovich Rozhdestvensky. A third species is considered dubious.
Saurolophus is known from material including nearly complete skeletons, giving researchers a clear picture of its bony anatomy. S. osborni, the rarer Albertan species, was around 9.8 meters long (32 feet), with its skull a meter long (3.3 feet). It weight is estimated at 1.9 tonnes (2.1 tons). S. angustirostris, the Mongolian species, was larger; the type skeleton is roughly 12 meters long (39.4 ft), and larger remains are reported. Aside from size, the two species are virtually identical, with differentiation hindered by lack of study.
The most distinctive feature of Saurolophus is its cranial crest, which is present in young individuals but is smaller. It is long and spike-like and projects upward and backward at about a 45 degree angle, starting from over the eyes. This crest is often described as solid, but appears to be solid only at the point, with internal chambers that may have had a respiratory and/or heat-regulation function.