The risk of infection in patients with primary immunodeficiency disease (PIDD) can be reduced through the use of immunoglobulin G (IgG) replacement therapy. Intravenous IgG (IGIV) products have been a mainstay of such treatment for many years. However, the IV route is not without its disadvantages, including the requirement for venous access, which can be problematic in some patients. Furthermore, large shifts in IgG levels during infusions may give rise to adverse effects at or just after peak as well as at low troughs. Subcutaneous IgG (IGSC), which is administered more frequently at lower doses, offers the advantage of avoiding high peaks and low troughs, thereby maintaining more consistent IgG levels and reducing systemic adverse effects. The SC route can also permit patients greater autonomy in their treatment of PIDD. When switching from IGIV, doses of IGSC should be individualized based on measured serum IgG levels and the clinical response of each specific patient.