PurposeThe safety and efficacy of subcutaneous immune globulin 20% (human) solution (Ig20Gly) were demonstrated in clinical trials. However, real-world evidence of the tolerability of self-administered Ig20Gly in elderly patients is lacking. We describe real-world patterns of Ig20Gly usage for 12 months in patients with primary immunodeficiency diseases (PIDD) in the USA.MethodsThis retrospective chart review of longitudinal data from 2 centers included patients aged ≥ 2 years with PIDD. Ig20Gly administration parameters, tolerability, and usage patterns were assessed at initial and subsequent 6- and 12-month infusions.ResultsOf 47 enrolled patients, 30 (63.8%) received immunoglobulin replacement therapy (IGRT) within 12 months before starting Ig20Gly, and 17 (36.2%) started IGRT de novo. Patients were predominantly White (89.1%), female (85.1%), and elderly (aged > 65 years, 68.1%; median age = 71.0 years). Most adults received at-home treatment during the study, and most self-administered at 6 months (90.0%) and 12 months (88.2%). Across all time points, infusions were administered at a mean rate of 60–90 mL/h/infusion, using a mean of 2 sites per infusion, on a weekly or biweekly frequency. No emergency department visits occurred, and hospital visits were rare (n= 1). Forty-six adverse drug reactions occurred in 36.4% of adults, mostly localized site reactions; none of these or any adverse events led to treatment discontinuation.ConclusionThese findings demonstrate tolerability and successful self-administration of Ig20Gly in PIDD, including elderly patients and patients starting IGRT de novo.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10875-023-01436-4.