Background/Aims Functional constipation (FC) is aa frequent functional gastrointestinal disorder, diagnosed according to the Rome criteria. In this study, we compared Rome III and Rome IV criteria for the diagnosis of FC, and determined the prevalence of FC according to these criteria. Methods Consecutive children between infancy and 17 years old were recruited for the study, excluding those with a known organic gastrointestinal disease. A prospective longitudinal design has beenused. For the diagnosis of FC, questionnaires on Pediatric Gastrointestinal Symptoms (QPGS) based on the Rome III and Rome IV criteria (QPGS-RIII and QPGS-RIV) were used. The agreement between these 2 questionnaires was measured by Cohen’s kappa coefficient. Results Two hundred fourteen children (mean age, 77.4 ± 59.5 months; 103 males) were screened. There was no statistically significant difference in the prevalence of FC evaluated using the QPGS-Rome IV vs the QPGS-Rome III in the overall sample (39/214 18.2% vs 37/214 17.3.0%; P = 0.831) as well as in any of the groups. The Cohen’s kappa test showed a good agreement between the 2 criteria (κ = 0.65; 95% CI, 0.51 to 0.78). Conclusion Our study demonstrates that the new Rome IV criteria have a good agreement with the Rome III criteria for the diagnosis of FC, without an increase in the number of potential diagnoses, despite the reduction in the duration of the symptoms. This conclusion is important in the management of childhood FC, since a late diagnosis negatively affects the prognosis. (J Neurogastroenterol Motil 2019;25:123-128)