A rare cause of intra-abdominal obstruction, mesenteric cysts derive from lymphatic tissue. The differential diagnosis should include mesenteric cyst when the patient presents with a history of multiple episodes of partial small-bowel obstruction or with an asymptomatic abdominal mass. A year-old girl was brought to the Family Practice Center with episodic, sharp, nonradiating, left-sided, mid-upper-abdominal pain. Examination indicated a possible diagnosis of mesenteric adenitis. Due to variation in the signs and symptoms of the condition, it appears that the use of ultrasonography is the most effective, nonoperative method of evaluation. Ultrasonography appears to be the most effective, nonoperative method of evaluation. Surgery is the only definitive diagnostic and therapeutic modality.