Laosaurus altus was named by Marsh (1878). Its type specimen is YPM 1876, a partial skeleton, and it is a 3D body fossil. Its type locality is Quarry 13, Como Bluff (YPM), which is in a Kimmeridgian/Tithonian crevasse splay sandstone/claystone in the Morrison Formation of Wyoming. It is the type species of Laosaurus.

It was misspelled as Laosaurus altas by Gegenbaur (1898); it was considered a nomen dubium by Bakker et al. (1990); it was recombined as Dryosaurus altus by Marsh (1894), Marsh (1896), Nopcsa (1901), Hay (1902), Nopcsa (1902), Lull (1911), Mook (1916), Gilmore (1925), Hay (1930), Swinton (1936), Avinoff (1940), Stokes (1949), Untermann and Untermann (1954), Tatarinov (1964), Kuhn (1964), Galton (1972), Galton and Jensen (1973), Galton and Jensen (1973), Galton (1975), Madsen and Miller (1979), Jurcsak and Popa (1979), Molnar (1980), Galton (1980), Galton (1981), McIntosh (1981), McGinnis (1982), Weishampel and Weishampel (1983), Galton (1983), Galton (1989), Sues and Norman (1990), Scheetz (1991), Weishampel and Heinrich (1992), Carpenter (1994), Chure et al. (1994), Ryan (1997), Naish and Martill (2001), Buchholz (2002), Norman (2004), Stanford et al. (2004), Mateus (2006), Chure et al. (2006), Pereda Suberbiola et al. (2006), Hübner and Rauhut (2007), Ruiz-Omeñaca et al. (2007), Ruiz-Omeñaca et al. (2007), Galton (2007), Butler et al. (2008), Galton (2009), Horner et al. (2009), Rich et al. (2010), McDonald et al. (2010), McDonald et al. (2010), Zheng et al. (2013), Becerra et al. (2016), Dieudonné et al. (2016), Herne et al. (2018), Xu et al. (2018), Carpenter and Galton (2018), Bell et al. (2018), Madzia et al. (2018), Herne et al. (2019), Cruzado-Caballero et al. (2019), Bell et al. (2019), Andrzejewski et al. (2019), Dieudonné et al. (2020), Dalla Vecchia (2020), Sánchez-Fenollosa et al. (2021), Rotatori et al. (2022).