A phylogeny of fifty-eight cockchafer species belonging to the genus Amphimallon Berthold, 1827 is proposed, based on sixty-five morphological characters. The cladistic analysis provides seventy-two equally parsimonious trees. The genus Amphimallon is redefined and species-groups are introduced and defined: A. pini-group (seven species), A. vernale-group (five species), A. solstitiale-group (seven species), A. arianae-group (two species), A. peropacum-group (one species), A. fuscum-group (eleven species), A. naceyroi-group (seven species), A. majale group (five species), A. lusitanicum-group (six species). Other species previously placed in Amphimallon are considered species incertae sedis in this paper: amphibolum Peyerimhoff, 1949, and a monophyletic group composed of six North African species: altifrons Baraud, 1971, julieni Baraud, 1972, melillanum Baraud, 1972, scutellare Lucas, 1846, subcristatum Fairmaire, 1879, subparallelum Escalera, 1913. Four new Amphimallon species are described: A. adanense sp. n. from Turkey, A. maniense sp. n. from Greece, A. jeannae sp. n. and A. safiense sp. n. from Morocco. The following taxonomic conclusions are proposed: A. seidlitzi Brenske, 1891 = A. trisinuatum Reitter, 1902 syn. n.; Amphimallon jeannei (Baraud, 1971) comb. n.; Miltotrogus caucasicus Gyllenhal, 1817 comb. n.; Amphimallon vernale (Brullé, 1832) stat. n.; A. furvum (Germar, 1817) stat. n.; A. javeti Stierlin, 1864 stat. n.