We present the case of a 13-year-old female with a 48-hour history of diffuse abdominal pain, fever, nausea, and vomiting, with worsening in the last few hours. On examination, she had signs of acute abdomen, and laboratory tests showed elevated acute phase reactants (APR). Abdominal ultrasound excluded acute appendicitis. A history of risky sexual behavior was reported, so pelvic inflammatory disease (PID) was considered. Although appendicitis is the most common cause of acute abdomen in adolescents, PID should be suspected in adolescents with risk factors. Prompt treatment is necessary to avoid possible complications and sequelae.