ABSTRACTAIM:The purpose of our study was to investigate the relation between serum Toxoplasma gondiiIgG antibodies in children and attention deficit hyperactivity disorder (ADHD) and its severity.METHOD:214 subjects, consisting of 107 children aged 6–18 and diagnosed with ADHD and 107 children with no ADHD or psychiatric pathology were included. Subjects underwent a detailed psychiatric examination based on DSM-V-TR diagnostic criteria, using a data form, the Kiddie Schedule for Affective Disorders and Schizophrenia Present and Lifetime Version (K-SADS-PL) for School-Aged Children (6–18), the DuPaul ADHD Rating Scale, Parent Rating Scale, the Conners Teacher Rating Scale (CTRS), and the Conners Parent Rating Scale (CPRS). Blood anti-Toxoplasma IgG antibody levels were investigated. The data obtained were then subjected to statistical analysis.RESULTS:T. gondiiIgG antibodies were positive in 8 (7.47%) of the case group and positive in 3 (2.8%) of the control group. No statistically significant difference was determined between the case and control groups in terms of T. gondiiIgG positivity (p = .215). Higher levels of severe ADHD were determined in Toxoplasma IgG positive patients in the ADHD group compared to Toxoplasma IgG negative subjects, the difference being statistically significant (p = .005).CONCLUSION:No significant differences were determined between the case and control groups in terms of T. gondiiIgG positivity and ADHD. However, correlation was determined between ADHD severity and T. gondiiIgG positivity.