Specific antibody immunodeficiency (SAD) is a primary immunodeficiency disorder characterized by normal levels of serum immunoglobulins (IgG, IgA, and IgM) associated with a dysfunctional immune response. SAD is associated with recurrent infections in the setting of an insufficient response to polysaccharide vaccinations. Streptococcus pneumoniae is a well-established cause of respiratory infections in SAD. However, there has been a paucity of evidence of pneumococcal peritonitis in SAD patients, being reported as spontaneous in acquired immunodeficiency such as AIDS. We report the first case of S. pneumoniae-induced peritonitis as the presenting sign for SAD.