all authors of this article declare that they qualify for authorship as defined by icmje http://www.icmje.org/#author . each author has participated sufficiently in the study and take public responsibility for appropriate portions of the content of this article . as this is a case report without patient identifiers , approval from institutional review board ( irb ) is not required at our institution . to ensure the integrity and highest quality of cytojournal publications , the review process of this manuscript was conducted under a double blind model ( authors are blinded for reviewers and vice versa ) through automatic online system .
alveolar rhabdomyosarcoma is an uncommon tumor affecting adolescents and young adults that is only rarely encountered in body fluid cytology . 
 we report the cytological features of metastatic alveolar rhabdomyosarcoma in the ascitic fluid of a 17-year - old female patient , who had presented with abdominal distention , 21 months after being diagnosed with perirectal alveolar rhabdomyosarcoma . 
 the rare single neoplastic cells that were admixed with abundant reactive mesothelial cells were initially misinterpreted as reactive mesothelial cells . however , their neoplastic nature was established after a careful review of their cytological features and the performance of immunoperoxidase stains . compared to the reactive mesothelial cells that were present in the sample , the malignant cells were smaller , with less ample and more homogenous cytoplasm . 
 they had slightly larger , more hyperchromatic , and more frequently eccentric nuclei , with larger nucleoli . 
 this case highlights the potential pitfall of the misinterpretation of metastatic alveolar rhabdomyosarcoma cells for reactive mesothelial cells . 
 awareness of this potential diagnostic problem and recognition of the cytomorphological features of this neoplasm in the body fluids allows the identification of malignant cells , even when they are rare and intimately associated with mesothelial cells .