Smooth muscle hyperplasia of the small intestine occurred in an 18-month-old rhea (Rhea americana). The mucosal thickening was 2-3 mm, and the enlarged muscle layers averaged 5 mm thick. The intestinal villi were lengthened, pleated, and expanded by smooth muscle hyperplasia within the lamina propria. The prominent muscularis mucosa averaged 20 smooth muscle cells thick. The tunica muscularis had symmetrical hyperplasia of both the inner circular muscle layer, which had an excess of 220 cells, and the outer longitudinal muscle layer, which consisted of five to six large fascicles, each approximately 75 cells thick. The smooth muscle hyperplasia, without hypertrophy, in all intestinal muscle layers differs greatly from mammalian cases of smooth muscle hypertrophy, in which the increase in intestinal size results from smooth muscle hypertrophy of the tunica muscularis.