Gossypiboma” – retained foreign object (more frequently a surgical sponge) – is a rare complication of a surgical intervention, usually during an emergency or a time-consuming procedure. The clinical features include nonspecific general and digestive symptoms. Due to the surrounding inflammatory reaction, it leads to the formation of tumoral masses or fistulas, making the differential diagnosis even more difficult. We present the case of a 60-year-old woman with a history of diabetes, arterial hypertension and multiple surgical procedures of the upper abdomen, who was admitted for altered general state and a pain in the right upper and lower quadrant, where an abdominal mass that covered the skin and the right costal margin was found, mild fever and anemia. The MRI raises the suspicion of a sarcoma. The first surgical procedure (June 2014) uncovers a pus-filled collection which was drained resulting a fistula with a continuous secretion (the Pathology report suggested Actinomycosis). The patient received multiple antibiotics, without an improvement. In January 2015, a CT exam revealed a possible retained foreign object situated deeply in the hepatorenal recess. The patient had undergone surgery, through the peritoneal cavity, thus confirming the diagnosis, with the excision of the surgical sponge. The patient had a favorable postoperative course with the closure of the fistula. Even though the diagnosis of a retained foreign object may prove difficult, it needs to be taken into consideration for the differential diagnosis of any postoperative case presenting an abdominal mass, with inflammatory reaction and chronic post-excisional fistula.