Although ovine tonsils play a major role in prion diseases, their morphology is poorly documented and morphometric data are sparse. Therefore, a stereological assessment of the surface area of the palatine and pharyngeal tonsils of five sheep was performed. The epithelial surface area of both tonsils is considerably increased by the presence of tonsillar crypts and folds. The mean epithelial surface area of the paired palatine tonsil was 7.14 cm(2) and that of the pharyngeal tonsil was 23.5 cm(2). In comparison with the paired palatine tonsil, the volume of the pharyngeal tonsil was almost two times larger, whilst its surface area was more than three times larger.