In a series of 100 colorectal adenomas, 23 tubulo-villous adenomas were individualized through the identification of papillae as structures persisting for more than 100 microm in serial sections with a connective axis lined with epithelial cells. In these adenomas, the tubular and villous areas with the highest dysplasia were selected, and a morphometric analysis was undertaken to assess the Index of Structural Atypia, the Nucleo-Glandular Index, and the Nuclear Stratification Index. The AgNor count and the proliferating cell nuclear antigen (PCNA) Label Index (LI) also were performed. The overall mean of each of these indexes was significantly higher in the villous sector than in the tubular one (P < .001). In 16 cases, the semi-objective method of dysplasia gradation showed a superior degree in the papillary sector, whereas it showed an equal degree in the remaining seven lesions. The AgNOR count was significantly different in all cases, with higher values in villous sectors (P < .05). With the exception of one case, this was confirmed by the PCNA LI. The Stratification Index showed significantly different values in 20 cases, whereas the other morphometric indexes showed a less discriminatory result. Our findings objectively show that the degree of dysplasia in tubulo-villous adenomas should be analyzed in the villous sector. The existence of heterogeneous cellular populations has been confirmed both in the structural organization of cells and in some basic parameters such as the cell proliferation rate in colorectal adenomas. Our findings suggest that the occurrence of villous architectural growth is a secondary event in a tubular adenoma. Enhanced cellular proliferation of the villous area allows the progressive substitution of tubular structures.