The biological behaviour of the polyp depends entirely on its histological subtype. Adenomas are the classic precursors to carcinoma. Polyp biopsy can differentiate neoplastic (adenoma and carcinoma) from non-neoplastic polyps (hyperplastic, inflammatory, hamartomatous). Due to potential sampling error, biopsy does not always differentiate between adenoma and carcinoma. Our aim was to investigate the degree of this potential sampling error. We carried out a study to compare the results of biopsies vs. total tissue examinations in a cohort of 433 neoplastic polyps. In this study 18.5% of carcinomatous polyps show definitive malignant elements only when the entire polyp is presented to the pathologist. We have therefore adopted a special reporting template if the polypoidal tumour is either biopsied or incompletely excised. The study also showed that within adenomas there could be variance of architectural patterns between the biopsy and the whole specimen. In this series, biopsying malignant colonic polyps gives rise to 18.5% false negative results and therefore it is significantly less efficient in the diagnosis of malignancy compared to total polyp examination.