Mosaic trisomy 2 in second-trimester amniocentesis is a very rare aneuploidy. The outcome of the pregnancies is quite variable, spontaneous abortions are frequent. A 37-year old woman underwent amniocentesis at 18 weeks of gestation because of abnormal serum screening with single umbilical artery (SUA) and cardiac dextroposition in fetal ultrasound (USG), and the cytogenetic result was 47,XX,+2/46,XX. Repeated amniocentesis and simultaneously cordocentesis at 21 weeks of gestation were ended with the analyses of the same mosaic aneuploidy. In addition to SUA and cardiac dextroposition, diaphragmatic hernia was detected in USG examination that was confirmed by fetal magnetic resonance imaging. The pregnancy was terminated at 22 weeks of gestation. Prenatal diagnosis of two or more cells with trisomy 2 at amniocentesis with USG findings should alert the physician for clinically significant aneuploidy and the presence of low-level trisomy 2 mosaicism at amniocentesis should be confirmed.