A prospective, open-label, multicenter, single-arm, Phase III study evaluated the efficacy and safety of Hizentra ® , a 20% human IgG for subcutaneous administration, in 51 primary immunodeficiency patients over 40weeks. Patients previously on intravenous or subcutaneous IgG were switched to weekly subcutaneous infusions of Hizentra ® at doses equivalent to their previous treatment. IgG levels achieved with Hizentra ® were similar to pre-study levels with subcutaneous, and higher by 17.7% than pre-study levels with intravenous IgG. No serious bacterial infections were reported in the efficacy period. The rate of all infections was 5.18/year/patient, the rates of days missed from work/school, and days spent in hospital were 8.00/year/patient and 3.48/year/patient, respectively. Local reactions (rate 0.060/infusion) were mostly mild (87.3%). No serious, Hizentra ® -related adverse events were reported. Individual median infusion durations ranged between 1.14 and 1.27h. Hizentra ® maintained or improved serum IgG levels without dose increases and effectively protected patients against infections.