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Patau syndrome (trisomy 13) is usually associated with multiple malformations such as facial defect, skeletal anomalies, cardiac defect, midline anomalies and severe mental retardation. Sonographic evaluation of structural anomalies is useful to enable prenatal diagnosis of Patau syndrome, which is less detected in maternal serum screening. Although major structural anomalies would be easily detected on prenatal ultrasound, some abnormalities are subtle and result in late gestational age at diagnosis. Here we report a case of Patau syndrome with Robertsonian translocation, (13;13)(q10;q10) presenting with isolated omphalocele, which was detected at the third trimester.