The purpose of this study is to assess the long-term efficacy, tolerability, and safety of IgPro20 in subjects with primary immunodeficiency (PID) as an extension to the preceding follow-up study ZLB07_001CR (NCT01458171).

Inclusion Criteria:

• Subjects who have completed the preceding follow-up study ZLB07_001CR.
• Written informed consent by the subject/parent/legally acceptable representative. Written assent for an underage subject (≥7 years and <20 years of age at the time of obtaining informed consent), according to the competencies of the subject.

Exclusion Criteria:

• Pregnancy or nursing mother.
• Participation in a study with an investigational medicinal product (IMP) within 3 months prior to enrollment except for study ZLB07_001CR.
• Subjects who are planning to donate blood during the study.
• Known or suspected antibodies to the IMP, or to excipients of the IMP.
• Treatment with another immunoglobulin G (IgG) within 3 months prior to the study.