OBJECTIVE: To investigate the combined effect of flow cytometry (FCM) and image cytometry (ICM) on DNA aneuploidy and to further facilitate the prompt diagnosis of malignant effusion. STUDY DESIGN: In our cross-sectional study the DNA content of sediment cells of 203 peritoneal or pleural effusion samples were detected through FCM and ICM, respectively. The calculation of sensitivity, specificity, and ROC curves were used to study the value of FCM and ICM and the combination of these 2 methods on diagnosis. RESULTS: On detecting DNA aneuploidy, the sensitivity, specificity, and accuracy of FCM were 78.6%, 80.0%, and 79.2%%, respectively. And the above indexes of the image analyzer were 83.5%, 78.6%, and 81.3%, respectively. Either FCM or ICM has a higher sensitivity and specificity than those of cytological examination of effusion. Combined FCM with ICM, the value of sensitivity, specificity, and accuracy were increased to 92.2%, 86.3%, and 89.6%, respectively. CONCLUSION: The sensitivity and specificity were increased significantly after combining FCM and ICM, as compared to the conventional cytology test. The combined detection can be used to help clinically identify the nature of the peritoneal and pleural effusion, which helps to diagnose malignant effusion in time. © Science Printers and Publishers, Inc.