We have conducted a nationwide survey to define the first-line immunosuppressive treatment for idiopathic acquired pure red cell aplasia (PRCA) in Japanese adult patients diagnosed from January 1990 to December 2004. Questionnaires were sent to forty-seven medical centers and eighty-seven patients with acquired chronic PRCA from forty-seven institutions were registered in this retrospective study. Thirty-four patients (39%) were classified into idiopathic PRCA. Cyclosporine A (CsA), prednisolone (PSL) and cyclophosphamide (CY) were initially given to 20, 10 and 3 patients with idiopathic PRCA, respectively. One patient was treated with anabolic steroid as first-line therapy. The response rates with CsA and PSL were 80 and 60 %, respectively. All patients who had been resistant to PSL and two out of three CY-resistant patients were responsive to CsA. An anabolic steroid resistant patient also responded to CsA. Thus, CsA was used in twenty nine patients as a form of primary or salvage treatment with an 86 % clinical response rate. Nine out of 25 (36%) CsA-responders eventually relapsed and 12.5% of the patients relapsed during therapy. The median remission duration in the CsA responders was seven years. All PSL-responders were predicted to eventually relapse within 2 years, and four out of seven patients on prednisolone relapsed during maintenance therapy. All patients responded to CsA during their second and/or third remission induction with or without PSL. Overall survival was not different between the CsA- and PSL-responders. Although the difference in remission duration between both responders was not statistically significant (p<0.114), which was probably due to the limited number of patients included in the study, CsA may be a best first-line treatment option for Japanese idiopathic acquired PRCA.