Ticks parasitizing introduced white-tailed deer, Odocoileus virginianus (Zimmermann), on St. John, U.S. Virgin Islands, were recorded during and after drought conditions. Tick infestation prevalences were 22% at the start of the drought (July 2015), 66% at the height of the drought (March 2016), and 35% after the drought had ended (July 2016; n = 67 deer). Samples of ticks from 22 tranquilized deer in July 2016 revealed the presence of two species, the southern cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), and the tropical horse tick, Dermacentor (Anocentor) nitens Neumann. Both tick species have considerable veterinary importance, especially for cattle and horses, respectively, as nuisance biters and also as vectors of parasitic piroplasms or of Anaplasma marginale Theiler. All 22 deer examined were infested by R. microplus, whereas 14 (64%) of the samples also included specimens of D. nitens. Because of the large numbers of ticks recorded, wild deer on St. John could develop associated health problems (pruritis, alopecia, anemia, low weight gain, tick-borne pathogens and parasites) and could also serve as a source of these ticks for cattle and horses.