Ornithomimus altus was named by Lambe (1902). Its type specimen is NMC 930, a partial skeleton, and it is a 3D body fossil. Its type locality is below Berry Creek, Steveville (NMC), which is in a Campanian/Campanian terrestrial horizon in the Oldman Formation of Canada.

It was recombined as Struthiomimus altus by Osborn (1916), Moodie (1917), Abel (1924), Huene (1927), Van Straelen (1928), Moodie (1930), Stromer (1931), Huene (1934), Stromer (1934), Huene (1934), Lowe (1935), Kuhn (1939), Russell (1964), Russell (1966), Russell (1972), Osmólska et al. (1972), Drake (1980), Molnar and Pledge (1980), Molnar (1980), Nicholls and Russell (1981), DeCourten and Russell (1985), Gauthier (1986), Currie (1987), Mader and Bradley (1989), Sanz et al. (1992), Currie (1992), Derstler (1994), Pérez-Moreno et al. (1994), Pérez-Moreno and Sanz (1995), Osmólska (1997), Eberth (1997), Makovicky and Norell (1998), Currie (2000), Hurum (2001), Eberth et al. (2001), Rauhut (2003), Makovicky et al. (2004), Senter et al. (2004), Kobayashi and Barsbold (2005), Currie (2005), Kobayashi and Barsbold (2006), Turner et al. (2007), Longrich (2008), Buffetaut et al. (2009), Bronowicz (2011), Turner et al. (2011), Xu et al. (2011), Zanno et al. (2013), Poropat and Kear (2013), Currie and Koppelhus (2015), White et al. (2015), McFeeters et al. (2016), Serrano-Brañas et al. (2016), Claessens and Loewen (2016), van der Reest and Currie (2017), Averianov et al. (2017), Chinzorig et al. (2017), Hunt and Quinn (2018), Senter and Sullivan (2019).