RESUMEN
Abdominal actinomycosis is a rare condition caused by actinomyces species found in the normal flora of the oral cavity, gastrointestinal and genital tract. All cases reported describe localized forms demonstrating masses, pseudotumors or abscess during surgery or radiology studies and there are no reports about spontaneous peritonitis caused by actinomycetes. We report a case in which this disease present as symptomatic ascitic fluid infection refractory to antimicrobial therapy for intra- abdominal sepsis and detected during unsuspected cytology test. The case was successfully treated with a penicillin regimen. As a spontaneous peritonitis variety, the microbiology diagnosis remains difficult as we don't think in this form of abdominal actinomycosis not described previously in the literature. The present illustrative case strength the usefulness of cytology test in patients with suspected ascitic fluid infection refractory to a medical therapy.