Leiomyoma of the transverse colon is uncommon. The majorities of these lesions are clinically insignificant, being diagnosed incidentally. Symptomatic leiomyomas of the colon are less common; sporadic case reports have been described in the relevant literature. We describe an additional case of extraluminal transverse colon leiomyoma with necrosis and perforation. A 22-year old female patient complaining abdominal pain was admitted with the diagnosis of peritonitis. The intraoperative findings were: a transverse colon mass on the mesenteric wall, purulent fluid on the left flank and Douglas pouch. A transverse colon resection with primary anastomosis has been performed. The histological findings were consistent with extraluminal leiomyoma with necrosis. The postoperative period was uneventful and the patient discharged on the 9th postoperative day. During a 9 month followup the patient is free of disease recurrence. Although benign, colon leiomyoma may cause life-threatening complications, requiring emergency surgery.