A wild, adult, female Florida cooter (Pseudemys floridana floridana) was evaluated for injuries sustained after vehicular trauma. On presentation the turtle had a minimally displaced caudal carapacial fracture, marked hyphema in the right eye, epistaxis, and frank hemorrhage from the cloaca. Immediately following initial triage, the turtle laid eight eggs and produced seven more over 72 h. After approximately 3 wk of hospitalization and treatment, the turtle received access to an outdoor water enclosure. Positive buoyancy was observed and a large, gas-filled, Y-shaped structure was identified in the caudal coelom via computed tomography. Cloacoscopy confirmed right-sided accessory cystitis, secondary to a focal necrotic wound with a mixed bacterial infection. After wound debridement and 3 wk of antibiotic therapy, the patient successfully submerged, there was no gas present in the accessory bladders, and the previous necrotic wound showed excellent healing on recheck cloacoscopy. This is the first report of accessory cystitis in the literature and it should be considered a differential for positive buoyancy in chelonian species that possess accessory bladders.