It is known that lower lobe pneumonia may result in a picture of acute abdomen; however, it can be easily overlooked when there are no signs or symptoms of the respiratory system. This case has been reported to remind the reader of the possibility of lower lobe pneumonia in patients presenting with a picture of acute abdomen. A ten-year-old male patient presented to our emergency outpatient clinic with the symptom of severe stomach ache that had started 2 days previously. The abdominal examination showed sensitivity, rebound, and defense. The examination results for his respiratory system and other systems were normal. The anterior-posterior pulmonary x-ray and direct abdominal x-ray in standing position were normal. No signs of acute abdomen could be seen in his abdominal ultrasonography. Lower lobe pneumonia was identified in his abdominal CT. It is difficult to diagnose pneumonia in patients who present with a picture of acute abdomen if there are no symptoms and x-ray signs related to the respiratory system. Anamnesis and physical examination are key to reaching an accurate diagnosis in such patients; however, any delay in diagnosis can be prevented by requesting further studies such as CT if the diagnosis cannot be ascertained by physical examination.