Introduction and aim <p>This study aimed to investigate the effect of upper respiratory tract infections on serum antiseizure medication levels in children with idiopathic epilepsy and the relationship between that condition and inflammation.</p> Materials and methods <p>Forty-nine patients aged 2–18 years presenting to our paediatric neurology clinic who were under follow-up with a diagnosis of idiopathic epilepsy and who were receiving valproate or carbamazepine therapy were included in this study. All patients were using either valproic acid (<i>n</i> = 31) or carbamazepine (<i>n</i> = 18). Patients were evaluated at the time of presentation with symptoms of upper respiratory tract infection and during the control period one month later. Serum antiseizure medication, interleukin-17&#xa0;A and interleukin-23 levels, complete blood count, alanine transaminase levels, creatinine levels, albumin levels, erythrocyte sedimentation rates, and C-reactive protein levels were measured during infection and during the control period one month later. Simultaneous electroencephalography examinations were also performed.</p> Results <p>No provoked seizures occurred in any patient during the infection period. Serum valproic acid levels were higher in patients during the infection period than in those same patients during the control period after one month, although this difference was not statistically significant (<i>p</i> = 0.073). There was also no significant difference in carbamazepine levels (<i>p</i> = 0.484). While no difference was observed in the interleukin-23 values between the two periods in patients receiving valproic acid, these values were greater in the patients who received carbamazepine during the infection period (<i>p</i> = 0.039).</p> Conclusion <p>The findings of this study suggest that mild upper respiratory tract infections do not cause clinically significant alterations in serum valproate or carbamazepine levels.</p>