Sixty patients (16 children, 44 adults) participated in the study aiming at evaluating: (i) IgG levels when switching patients from intravenous IgG (IVIG) infusions in hospital to subcutaneous (SCIG) self-infusions at home using the same cumulative monthly dose, (ii) protections against infections, and (iii) safety of a new, ready-to-use 16% IgG preparation. All children and 33 adults had received IVIG therapy for >6 months at enrolment. Ten adults who had been on SCIG therapy for many years served as controls. Mean serum IgG trough levels increased in the pre-IVIG children from 7.8 to 9.2 g/L (non-inferiority: p < 0.001) and in the adults from 8.6 to 8.9 g/L (non-inferiority: p < 0.001). Totally 114 respiratory tract infections occurred, 90% of them mild. One serious bacterial infection (pneumonia) was reported for one adult. The annualized rate of serious infections was 0.04 episodes/patient. In total 2297 infusions were given and 28 (1%) systemic adverse reactions occurred, none of them severe. Local tissue reactions declined over time, this being particularly distinct after 8 to 10 weeks. In conclusion, the SCIG administration route was safe. High IgG levels were easily maintained resulting in a very good protection against infections.