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INTRODUCTION The utility of cytologic evaluation of effusion fluids in adults is well established but has been less well documented in the pediatric population. We examined the clinicopathologic characteristics of children with malignant effusions to establish the value of cytologic examination of these specimens. MATERIALS AND METHODS Pleural, pericardial, peritoneal, and intraoperative washing specimens obtained between January 2000 and October 2015 were identified via surgical pathology database search. Relevant clinical and pathologic data was recorded. Statistical analysis of patient groups was performed via two-sided heteroscedastic Student t tests, and Kaplan-Meier analysis was used to compare overall survival between patient groups. RESULTS 474 effusion/washing specimens obtained from 342 patients were identified: 179 pleural effusions, 220 peritoneal fluids, 28 pericardial effusions, and 47 intraoperative washing specimens. Of these, 13.7% (56 of 474) effusion specimens were positive for malignancy. Among cancer patients with effusions, malignant effusions were seen in 54.5% of patients with rhabdomyosarcoma and 28.8% of patients with hematolymphoid malignancies. Regarding patient outcomes, malignant effusions were associated with statistically significantly shorter overall survival (P = 0.019). When compared with stage IV patients with benign effusions, those with malignant effusions had a shorter 5-year overall survival (P = 0.042); multiple malignant effusions were associated with a dramatically shorter survival than a single malignant effusion. CONCLUSIONS The overall rate of malignant effusions in our patient population was 13.7%. Malignant effusions in children, particularly multiple, portend a poor prognosis. Our observations emphasize the importance of accurate cytologic diagnosis of effusion fluids, and reinforce the value of their cytologic evaluation.