This study aimed to determine the prevalence of infantile functional gastrointestinal disorders (FGIDs) based on Rome IV diagnostic criteria, and to determine the associated patient demographic and nutritional characteristics. A total of 2383 infants aged 1-12 months which were evaluated by 28 general pediatricians and pediatric gastroenterologists on the same day at nine tertiary care hospitals around Istanbul, Turkey, between November 2017 and March 2018, were included in the study. Patients included consulted the pediatric outpatient clinics because of any complaints, but not for vaccines and/or routine well child follow-ups as this is not part of the activities in the tertiary care hospitals. The patients were diagnosed with FGIDs based on Rome IV diagnostic criteria. The patients were divided into a FGID group and non-FGID group, and anthropometric measurements, physical examination findings, nutritional status, risk factors, and symptoms related to FGIDs were evaluated using questionnaires. Among the 2383 infants included, 837 (35.1%) had >= 1 FGIDs, of which 260 (31%) had already presented to hospital with symptoms of FGIDs and 577 (69%) presented to hospital with other symptoms, but were diagnosed with FGIDs by a pediatrician. Infant colic (19.2%), infant regurgitation (13.4%), and infant dyschezia (9.8%) were the most common FGIDs. One FGID was present in 76%, and >= 2 FGIDs were diagnosed in 24%. The frequency of early supplementary feeding was higher in the infants in the FGID group aged <= 6 months than in the non-FGID group (P = 0.039).