INTRODUCTION: Sclerosing encapsulating peritonitis (SEP) is a rare condition causing intestinal obstruction. A thick fibrous membrane envelops abdominal organs. SEP is classified into two types: abdominal cocoon syndrome (ACS), also called idiopathic or primary SEP, and secondary SEP. Symptoms range from subacute to acute intestinal blockage, and diagnosis is usually confirmed during laparotomy. CASE PRESENTATION: The authors present a case of a 32-year-old woman who presented with intermittent per-vaginal bleeding for 1 month, abdominal distension, decreased appetite, and significant weight loss over 5 months. Examination revealed pallor and a palpable 12×12 cm mass in the right lower abdomen. Imaging revealed a lobulated mass in the mid-ileum with bowel wall thickening. She underwent laparotomy, revealing fibrous tissue, and a nodular mass on the distal ileum. Histopathology confirmed non-Hodgkin's lymphoma. DISCUSSION: Sclerosing encapsulating peritonitis is a rare chronic inflammatory condition affecting the peritoneum. Primary SEP, also known as abdominal cocoon or idiopathic SEP, lacks a definitive cause, while secondary SEP results from conditions like peritoneal dialysis, liver cirrhosis, and malignancies. It involves peritoneal irritation leading to inflammation, fibrin-like material release, and subsequent bowel encasement and fibrosis. Diagnosis is typically made during laparotomy, though contrast-enhanced CT scan aids in presumptive diagnosis. CONCLUSION: This case report highlights a rare occurrence of abdominal cocoon syndrome in a patient with non-Hodgkin B-cell lymphoma, presenting with abdominal pain, distension, and bowel obstruction. Diagnosing this condition early is crucial, especially in patients with underlying malignancies. More research is needed to improve management.