Patients with specific antibody deficiency (SAD) have a deficient immunologic response to polysaccharide antigens. Such patients experience sinopulmonary infections with increased frequency, duration, or severity compared with the general population. SAD is definitively diagnosed by immunologic challenge with a pure polysaccharide vaccine in patients 2 years old and older who have otherwise intact immunity, using the 23-valent pneumococcal polysaccharide vaccine as the current gold standard. Specific antibody deficiencies comprise multiple immunologic phenotypes. Treatment must be tailored based on the severity of symptoms. Most patients have a good prognosis. The deficiency may resolve over time, especially in children.