Objective To validate the Quintero stage III subclassification for twin–twin transfusion syndrome (TTTS) based on visibility of the bladder of the donor twin. Methods Between July 2002 and August 2006, there were 131 pregnant Japanese women affected by severe TTTS before 26 weeks' gestation, treated with fetoscopic laser surgery at five centers in Japan, whose pregnancies continued beyond 22 weeks. Outcome data were available in all cases and surviving infants were followed up for at least 6 years. This study focused on the Stage III TTTS patients. These were subclassified into Stage III atypical (abnormal Doppler flow with visible donor bladder) and Stage III classical (abnormal Doppler flow with non‐visible donor bladder) groups. Perioperative data and postnatal outcomes were compared between the groups. Results Seven Stage I, 22 Stage II, 82 Stage III and 20 Stage IV pregnancies continued beyond 22 weeks. There was a significantly higher incidence of absent or reversed end‐diastolic velocity in the umbilical artery (UA‐AREDV) of the donor in Stage III atypical than in Stage III classical patients (83.8% vs. 53.3%, P = 0.004). Stage III atypical cases also had a significantly higher incidence of arterioarterial (AA) anastomoses (72.9% vs. 17.8%, P < 0.001) and intrauterine fetal demise (IUFD) of the donor (43.2% vs. 13.3%, P = 0.002). However, there were no differences in overall survival or in abnormal brain scans of surviving infants. Donors with both UA‐AREDV and AA anastomoses had a significantly higher incidence of IUFD compared with the others (53.3%, P < 0.001). Conclusions Quintero stage III atypical was characterized by a high incidence of AA anastomoses and UA‐AREDV of the donor, resulting in IUFD. Subclassification of Stage III based on visibility of the bladder of the donor twin was adequate for and compatible with differentiating prognosis and pathophysiology. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.