Temporomandibular joint (TMJ) disorders (TMD) are usually diagnosed based on the patient's clinical findings and the results of image investigations; however, understanding of the inflammatory process in TMJ is difficult. In addition, many of the TMJ disease types share common principal symptoms. Therefore, TMJ diseases in the early stage can be misdiagnosed with TMD. It is hypothesized that cytopathologic examination of the joint lavage fluids is useful in interpreting the TMD-associated inflammatory process from a cellular aspect. The aim of this study was to assess the TMJ lavage fluid cytopathologically in TMD patients. Thirty-nine patients, clinically diagnosed as TMD, were included in the present study. Clinical symptoms of the patients were recorded. Forty-four samples of TMJ lavage fluid were collected and paraffin-embedded cell sections were made by cell block tissue array method. Cytologic conditions in upper articular cavity of TMJ were cytopathologically diagnosed and were compared with the clinical symptoms of each patient. Cell components were detected in 22 of the 44 analyzed joint lavage fluids. There was a correlation between cytopathologic findings and clinical symptoms. Variety of cytopathology and inflammatory conditions in patients with similar clinical symptoms were also found. The results suggested that cytopathologic examination of the joint lavage fluids from TMD patients is helpful for gaining an understanding of the inner local conditions of TMJ at the cellular level. Diagn. Cytopathol. 2014;42:30–36. © 2013 Wiley Periodicals, Inc.