Colorectal adenomas are usually classified into two categories: tubular and villous adenomas. A mixed (tubulovillous) phenotype is also recognized. Two other histological phenotypes, namely serrated and microtubular adenomas, have been reported in the literature but neither have been included in large series. In this survey, all colorectal adenomas seen at this Department between 1993 and 2000 (n = 3135) were classified into the above 5 histological categories. The results showed that 66% (n = 2074) were tubular, 9% (n = 281) villous, 18% (n = 551) mixed, 6% (n = 202) serrated and the remaining 1% (n = 27) microtubular. More than 80% of the tubular, villous, serrated and microtubular adenomas were located in the colon. None of the microtubular adenomas were found in the rectum. The molecular signals whereby the colorectal mucosa in some patients "etch" serrated or microtubular neoplastic structures whereas in others tubular or villous neoplastic structures, have not been explored. One possible explanation might be that the pathway followed by the cascade of committed molecular events is less "accessible" for the "etching" of serrated and microtubular structures or that the process is less complex for the molecular design of tubular and villous configurations.