To provide practical guidelines for the cytopathologic diagnosis of malignant mesothelioma (MM). Cytopathologists involved in the International Mesothelioma Interest Group (IMIG) and the International Academy of Cytology (IAC), who have an interest in the field contributed to this update. Reference material includes peer-reviewed publications and textbooks. This article is the result of discussions during and after the IMIG 2012 conference in Boston, followed by thorough discussions during the 2013 IAC meeting in Paris. Additional contributions have been obtained from cytopathologists and scientists, who could not attend these meetings, with final discussions and input during the IMIG 2014 conference in cape town. During the previous IMIG biennial meetings, thorough discussions have resulted in published guidelines for the pathologic diagnosis of MM. However, previous recommendations have stated that the diagnosis of MM should be based on histological material only. ^[1],[2] Accumulating evidence now indicates that the cytological diagnosis of MM supported by ancillary techniques is as reliable as that based on histopathology, although the sensitivity with cytology may be somewhat lower. ^[3],[4],[5] Recognizing that noninvasive diagnostic modalities benefit both the patient and the health system, future recommendations should include cytology as an accepted method for the diagnosis of this malignancy. ^[6],[7] The article describes the consensus of opinions of the authors on how cytology together with ancillary testing can be used to establish a reliable diagnosis of MM.