Postinfectious autoimmunity has been implicated in Tourette’s syndrome and obsessive-compulsive disorder (TS/OCD), whereas increased frequency of upper respiratory tract infections (URTI) in TS/OCD patients suggests immune deficiency. We hypothesized that antineuronal antibodies may be elevated in patients (reflecting autoimmune processes), and levels of total immunoglobulins (Igs) may be decreased (reflecting immune deficiency). We analyzed plasma of TS/OCD patients (n = 24) and healthy age- and sex-matched control subjects (n = 22) by enzyme-linked immunosorbent assay (ELISA) for the levels of total and specific IgG, IgM, and IgA against antigens previously identified in multiple sclerosis (myelin basic protein and myelin-associated glycoprotein) and Sydenham’s chorea (ganglioside-GM1, lysoganglioside, and tubulin). Total IgA was decreased in TS/OCD patients (median 115 mg/100 mL) compared with control subjects (141 mg/100 mL; p = .02). Specific IgA against all antigens, except tubulin were also decreased in the patients (MPB 0 vs. 13 [ELISA units [EU]; myelin-associated glycoprotein 29 vs. 44 EU, p = .04; ganglioside GM1 21 vs. 35 EU, p = .01; lysoganglioside 44 vs. 56 EU, p = .03; tubulin 44 vs. 44 EU, p = .8). The levels of total IgA and anti-myelin basic protein (MBP) IgA were significantly lower in the subgroup of pediatric autoimmune neuropsychiatric disorder associated with Streptococcus (PANDAS) cases (n = 10) than in non-PANDAS cases (n = 9; total IgA 98 mg/100 mL vs. 133 mg/mL, p = .03; anti-MBP IgA 1 vs. 6 EU, p = .03) or healthy control subjects (total IgA 141 mg/100 mL, p = .02; anti-MBP IgA 13 EU, p = .005). At least some TS/OCD patients may suffer IgA dysgammaglobulinemia, possibly rendering the children more prone to URTI.