Although often overlooked immune deficiencies are more common than generally believed. The internist is frequently the first physician to potentially meet affected patients, playing a significant role in detecting these immune deficiencies, whether they are primary (congenital) or secondary (acquired). In both scenarios, early identification and intervention can greatly reduce the morbidity and mortality of these patients. In this article, we review common immune deficits, suggest initial assessments when indicative signs are present, and provide guidance for management.