A systematic revision of the mealybug genus Delottococcus Cox & Ben-Dov is presented. Nine species are treated, including D. millari which is described as new. The eight previously described species are: Delottococcus aberiae (De Lotto), D. confusus (De Lotto), D. elisabethae (Brain), D. euphorbiae (Ezzat & McConnell), D. phylicus (De Lotto), D. proteae (Hall), D. quaesitus (Brain), and D. trichiliae (Brain). Adult females of all species are described and illustrated and a key for their identification is presented. In the past, specimens determined as D. elisabethae have been recorded from citrus and other hosts, but these appear to be misidentifications of D. aberiae. Delottococcus elisabethae is only known from the original collection. As invasive species, D. confusus is reported from California and Hawaii, D. aberiae from Spain, and D. euphorbiae from France, Italy, and Sicily.