The present study evaluated the effect of sodium saccharin on mouse tracheal epithelium, in relation to its possible structural alterations. Mice of the C3H strain were fed with standard pellets supplemented with sodium saccharin for 180 days. At that time the mice were sacrificed and their trachea were processed for transmission electronic microscopy. We demonstrated that sodium saccharin produces alterations in cellular surface cilia, with cytoplasmic excrescences and ciliary malformations. These results suggest that sodium saccharin is not an innocuous sweetener and that it may cause structural alterations in epithelial tissues.