Treatment of primary immunodeficiency (PI) is typically initiated with intravenous immunoglobulin (IVIG) loading and then continued with IVIG or subcutaneous IgG (SCIG). This prospective, open-label, multicenter, 6-month study evaluated a new regimen of initiating IgG therapy with SCIG in 18 previously untreated patients. In the loading phase, SCIG 100 mg/kg was administered for five consecutive days (total loading dose 500 mg/kg). During the maintenance phase, patients self-infused SCIG 100 mg/ kg/week at home. The primary efficacy endpoint of IgG levels ≥5 g/L on day 12 was achieved in 17 patients (94.4%; 95% CI 0.727, 0.999). The rate of infections was 3.95 episodes/patient/year. Improvement was found in many subscales of the health-related quality of life questionnaires. SCIG treatment was well tolerated, with no related serious adverse events (AEs). Nine (50%) patients experienced related AEs, including local reactions (rate 0.105 events/infusion). The results suggest that therapy of newly diagnosed patients with PI can be initiated directly with SCIG.