The morphogenesis of minute colonic adenomas was investigated by complete serial sectioning of human tissues from 4 individuals with familial polyposis coli. Minute adenomas, consisting of a few atypical glands, were located in the upper part of the mucosa. Single-gland adenomas, consisting of single atypical glands, also were located in the upper to superficial part of the mucosa with endophytic growth. Twelve lesions smaller than single-gland adenomas also were detected. These lesions, buds of single-gland adenomas, consisting of epithelial clusters with mild atypia, were located in the middle part of the mucosa and had sprouted from normal crypts to the lamina propria. The conclusion was that buds of single-gland adenomas originate in the proliferative zone of normal crypts, sprout out of the lamina propria mucosae, move upward with migration of the epithelial cells of the crypts, and are identified as single-gland adenomas in the upper part of the mucosa.