A 12-year-old Standardbred mare was evaluated for colic. An intra-abdominal mass causing jejunal obstruction was found during emergency exploratory celiotomy. Following surgical removal of the mass, the mare made a full recovery, and the mass was determined to be an abscess. Initial aerobic culture of the abscess revealed Rhodococcus equi, and it was suspected that this was a rare case of Rhodococcus equi infection in an adult horse. Anaerobic culture results and histopathologic evaluation of the abscess instead proved that the abscess was secondary to intestinal perforation and contamination of the peritoneal cavity by enteric bacteria.