The paper describes a case of Pelvic Inflammatory Disease (PID) in a fourteen-year-old girl who presented with salpingitis, low abdominal pain, fever, high inflammation indexes and infection by Chlamydia trachomatis and Gardnerella. As guidelines suggest, she was treated with doxycycline, metronidazole and ceftriaxone and her clinical conditions rapidly improved. PID can develop also in teenagers, especially if sexually active, and it must be differentiated from other causes of acute abdomen. The diagnosis can be based on the presence of pain and on at least one criterion between clinical objectivity (fever, vaginal secretions) and laboratory data (vaginal swab, blood exams, vaginal secretion microscopic analysis). Instrumental exams can support the diagnosis but sometimes only laparoscopy and biopsy can reveal a condition of PID. Adequate antibiotic treatment should be performed to avoid complications over future reproductive life.