Background: It is suggested that constipation could be due to celiac disease (CD); therefore, this study aimed to determine the prevalence of positive tissue transglutaminase (tTG) IgA test among children with functional constipation (FC). Methods: In this case-control study, 182 consecutive patients with FC who fulfilled the Rome III criteria as cases were compared with 240 healthy children as the control group in terms of suspicious CD by measuring the serum tTG IgA level. Results: There was a significant difference in favor of the case group in terms of serum tTG IgA levels (P = 0.000). The probability of having CD would change based on belonging to each group (case/control odds ratio [OR] = 0.222). Conclusion: With respect to these data, tTG IgA level was observed to be significantly higher in patients relative to healthy children; therefore, it is recommended that patients be screened for CD through the tTG IgA.