Disorders of urachal remnants are uncommon. While a urachal cyst usually is asymptomatic, infection may mimic a variety of acute intra-abdominal or pelvic processes. We describe 10 patients in 2 distinct age groups (the young child and the young adult) with an infected urachal cyst. The presenting symptoms and signs in most patients included dysuria, severe lower abdominal pain and fever. In 7 patients the correct preoperative diagnosis was made. Diagnoses at referral included Crohn's disease, bladder carcinoma and pelvic inflammatory disease. A single procedure was performed in 7 cases and a staged technique was used in 3. The differential diagnosis of acute abdominal and pelvic pain or a midline lower abdominal mass in the pediatric or young adult age group should include infection of a urachal remnant.