Pachycephalosauria was named by Maryańska and Osmólska (1974). It was considered monophyletic by Butler et al. (2008).

It was reranked as the infraorder Pachycephalosauria by Cooper (1985); it was reranked as the unranked clade Pachycephalosauria by Sereno (2000), Buchholz (2002), Butler et al. (2008), Han et al. (2012) and Dieudonné et al. (2020).

It was assigned to Neornithopoda by Cooper (1985); to Ornithischia by Maryańska and Osmólska (1974), Zhao (1983), Russell (1984), Maryanska and Osmólska (1985), Carroll (1988) and Peng et al. (2001); and to Marginocephalia by Sereno (1986), Sues and Galton (1987), Benton (1990), Dodson (1990), Olshevsky and Ford (1994), Sereno (1997), Sereno (1998), Sereno (1999), Sereno (2000), Buchholz (2002), Weishampel (2004), Xu et al. (2006), Butler et al. (2007), Butler et al. (2008), Han et al. (2012) and Dieudonné et al. (2020).