To evaluate the long-term efficacy and safety after the end of romiplostim treatment by observation [up to 5 years] of patients who were registered for Study 531-003/531-004 in immunosuppressive therapy-naïve patients with aplastic anemia.

Inclusion Criteria:

• Patients whose written consent to participate in this research was obtained among patients registered for Study 531-003/531-004
• Of the patients who died before their consent to participate in this research was obtained among those registered for Study 531-003/531-004, patients whose legally authorized representatives such as their family had given the consent or patients whose legally authorized representatives had not refused in the disclosure of information by opt-out
• Of the patients who died before their consent to participate in this research was obtained among those registered for Study 531-003/531-004, patients, patients for whom the consent process exemption was approved by the Ethics Review Committee, etc. of the participating medical institutions at the participating medical institutions in the countries without the opt-out system

Exclusion Criteria:

• Patients who are judged by the investigator or sub-investigator to be unfavorable for participation in this research

Patients enrolled in Study 531-003/531-004