A questionnaire survey of Japanese patients with thrombotic microangiopathy (TMA) was carried out to investigate the frequency, laboratory abnormalities, and outcome in 2004. Out of 185 patients, there were 13 with familial TMA and 172 with acquired TMA. In acquired TMA, there were 66 with Escherichia coli O-157 infection (O-157)-related TMA, 35 with ADAMTS13-related TMA, and 22 with other types of TMA. The frequency of TMA in O-157-related TMA was high in patients from 0- to 15-year-old, and acquired TMA without O-157 was frequently observed in patients ranging from 31 to 65 years of age. In the treatment of acquired TMA, including plasma exchange (PE), steroid, antiplatelet agent, and anticoagulant, PE was carried out in 94.3% of ADAMTS13-related TMA, 77.3% of other TMA, and 7.6% of O-157-related TMA. The efficacy of PE and steroid therapy tended to be higher in ADAMTS13 TMA than in other types of TMA. The complete remission rate is the highest in O-157 TMA. The mortality rate was the lowest for O-157 TMA, and this rate also tended to be lower in ADAMTS13-related TMA than in other types of TMA. However, the determination of ADAMTS13 was not universal in Japan at the time of this questionnaire.