Sulawesi tortoise adenovirus-1 (STAdV-1) is a newly discovered virus infecting endangered and threatened tortoises. It was initially described from a confiscated group of 105 Sulawesi tortoises (Indotestudo forsteni) obtained by the Turtle Survival Alliance and distributed to five sites with available veterinary care across the United States. In a 3-yr period from the initial outbreak, one multi-species collection that rehabilitated and housed adenovirus-infected Sulawesi tortoises experienced deaths in impressed tortoises (Manouria impressa) and a Burmese star tortoise (Geochelone platynota). Impressed tortoises that died had evidence of systemic viral infection with histopathologic features of adenovirus. Adenovirus was identified by consensus nested polymerase chain reaction (PCR) testing and subsequent sequencing of PCR products. Sequencing indicated that the adenovirus infecting these impressed tortoises and Burmese star tortoise was STAdV-1. In one impressed tortoise, viral infection was confirmed using transmission electron microscopy. In situ hybridization using a semiautomated protocol and fluorescein-labeled riboprobe identified STAdV-1 inclusions in spleen, liver, kidney, and testis of one impressed tortoise. The impact of this virus on captive and wild populations of tortoises is unknown; however, these findings indicate that STAdV-1 can be transmitted to and can infect other tortoise species, the impressed tortoise and Burmese star tortoise, when cohabitated with infected Sulawesi tortoises.