There are numerous diseases associated with the pleura; Cytodiagnosis, by visual analysis of cells, Establishes with some degree of precision the presence of malignant neoplasia, replacing invasive procedures Such as surgery. This analysis has very low sensitivity rates between 50% and 80% and specificity of 97%, Which leads to the late diagnosis of tumors, in the first case, or to the suspicion of neoplastic lesions that do not exist, in the last. The present project provides a computer support that allows the specialists to take better Decisions for cytologic diagnosis. With the intervals of each cellular morphological parameter was determined The performance of the Knowledge Based System, which found nuclei with low levels of gray, small, Central or slightly eccentric, regular contour, homogeneous chromatin, scarce, round cytoplasm with Nucleus / cytoplasm ratio between 1: 5-1: 2, parameters exposed by specialized medical literature of cells Mesothelial cells.