The South American genus Allorrhina Burmeister (Coleoptera: Scarabaeidae: Cetoniinae: Gymnetini) is comprehensively revised. Redescriptions, diagnoses, distributions, and illustrations of nine species are provided. Allorrhina denotata Abadie and Ratcliffe from Brazil is described as a new species. The following new synonyms are established: Cotinis amazonica Thomson is Allorrhina carmelita (Burmeister); Gymnetis rhinoceros Gory and Percheron, Gymnetis cornifrons Gory and Percheron, Allorrhina baeri Bourgoin, Allorrhina viridicans Bourgoin, and Allorrhina gounellei Bourgoin are all Allorrhina menetriesii (Swederus); Gymnetis lugubris Thomson is Allorrhina nigerrima Burmeister.