We set out to determine the frequency of chronic reversal twin-twin transfusion syndrome in a large cohort of prospectively studied cases of twin-twin transfusion syndrome (TTTS) and to look for any unusual anastomotic configuration in postnatal injection studies and underlying structural anomalies or aneuploidy. Fifty-seven cases of TTTS were seen over 3 years at the Centre for Fetal Care. They had serial ultrasound scans for growth, liquor volume and Doppler assessment of the fetal circulation. They had amnioreduction, septostomy and/or selective reduction when appropriate. Placental anastomotic configurations were compared between the cases of reversal of TTTS and control TTTS cases. Five per cent of the 57 cases seen in our unit seen over a 3-year period had documented reversal. Frequency of aneuploidy/structural anomalies in this cohort of three cases is higher compared to control TTTS (67% vs. 11%, P < 0.05). Vascular anatomy of the three cases does not differ from the control TTTS cases.