Yankee Penny, a 3 year old, female, intact Thoroughbred racehorse presented to the Cornell University Large Animal Medicine service on 6/8/2005 with a chief complaint of colic. The day prior to presentation, Yankee Penny had developed a fever and was diagnosed with epiglottitis, and started on 20 grams of chloramphenicol by mouth four times a day. Two other horses from the same barn were also diagnosed with epiglottitis and started on chloramphenicol on 6/7/2005. Both of these horses also developed signs of colic and were sent to another referral hospital. Yankee Penny was observed overnight and developed acute laminitis the following morning. The other two horses also developed acute laminitis. A chloramphenicol compounding error was suspected but was not substantiated. This case report describes a case of acute laminitis in a Thoroughbred filly. A brief discussion of the current theories of laminitis pathogenesis and how this information was utilized in the selection of treatment for Yankee Penny is included.