Chlamydia trachomatis is a well-known cause of acute and chronic salpingitis, accounting for approximately half of all cases of pelvic inflammatory disease. Typically, patients with acute chlamydial salpingitis present with acute lower abdominal pain, tenderness on bimanual pelvic examination, or vaginal discharge. We describe a case of acute chlamydial salpingitis with marked ascites and an adnexal mass that simulated a malignant neoplasm. Microscopically, a severe lymphofollicular salpingitis and a marked lymphofollicular hyperplasia of the omentum and retroperitoneal lymph nodes were found. Chlamydial inclusions in the fallopian tube epithelium were demonstrated by immunohistochemistry using a mouse monoclonal antibody to a genus-specific outer membrane lipoprotein. Chlamydial infection may cause marked ascites and a palpable adenexal mass and should be considered whenever marked chronic inflammation with a lymphofollicular hyperplasia involves the fallopian tube or other female genital tract sites.