Given the importance of viral, bacterial and fungal diseases in agriculture and their impact on crop yields, this study evaluated leaf ultrastructural changes in sugarcane varieties infected by these diseases, aiming to find morphological responses that may be associated to the decline of sugarcane yield. Three independent experiments were carried out with sugarcane varieties. In the three experiments, a randomised block design was used with 10 replications. The treatments consisted of the following diseases: mosaic from infection of variety SP86-155 by SCMV (experiment 1); stunting from infection with bacterium Leifsonia xyli subsp. xyli and smut from infection with fungus Sporisorium scitamineum (formally called Ustilago scitaminea) in the variety SP70-3370 (experiment 2); and scald from infection of variety SP78-5495 by bacterium Xanthomonas albilineans (experiment 3). The ultrastructural parameters were evaluated: mesophyll thickness, xylem diameter, phloem beam diameter, epidermal thickness of the adaxial face, epidermal thickness of the abaxial face, cuticle thickness of the adaxial face and cuticle thickness of the abaxial face. Healthy plants were controls for the three experiments. Sugarcane plants with mosaic, stunting, smut and scald diseases show deleterious changes in leaf ultrastructure.