BACKGROUND Anterior sacral meningocele (ASM) is a defect in the closure of the neural tube. Patients can be asymptomatic or present with genitourinary, neurological, reproductive, or colorectal dysfunction. Magnetic resonance imaging (MRI) is the gold standard test because it can assess communication between the spinal subarachnoid space and the lesion and identify other abnormalities. Surgical correction is the definitive treatment because untreated cases have a mortality rate of more than 30%. OBSERVATIONS A 24-year-old woman with Marfan syndrome presented with polyuria, recurrent urinary tract infections, and renal injury for 3 months along with a globose abdomen, with a palpable mass in the middle and lower third of the abdomen that was massive on percussion. MRI showed an ASM consisting of two cystic lesions measuring 15.4 × 14.3 × 15.8 and 6.7 × 6.1 × 5.9 cm, respectively, compressing the distal third of the right ureter and causing a hydroureteronephrosis. Drainage and ligature of the cystic lesion were performed. The urinary outcome was excellent, with full recovery after surgery. LESSONS ASM should be suspected in all abdominal masses with progressive symptoms in the setting of Marfan syndrome. Computed tomography and MRI are important to investigate genitourinary anomalies or other types of dysraphism to guide the best surgical approach.