A colonic enterolith was necropsied in an 11-year-old pony with a 2-week history of mild, intermittent colic. The enterolith was in the distal portion of the large intestine. A 2.1-kg, greenish-gray, rugby ball-sized (19 cm × 15 cm × 12 cm) stone was extracted from the intestine. Analysis of the component elements revealed 100% magnesium ammonium phosphate (struvite). Enterolithiasis commonly affects Arabian horses, and most horses with enteroliths are ~10 years of age. Enterolithiasis is associated with recurrent colic. This is the first report of a colonic stone in a pony.