We compared the contraction of round, square, and triangular abdominal stomas of isolated ileal segments. Twelve stomas of each of these three different shapes were observed in six dogs for periods ranging from 1 to 4 months. Our observations indicate that the square shaped enterocutaneous stoma is preferable to the more conventional circular one. The square shape provides the longest perimeter for a given surface area with minimum contraction, whereas the circle has the shortest perimeter and results in maximum contraction.