The aims of the study were to identify the frequency and causes of chronic abdominal pain in a large academic primary care population at the University of Iowa Children’s Hospital. We evaluated retrospectively the complete charts of children ≥4 years old, seen for at least one health maintenance visit in the primary paediatric clinic during a 6-month period, for complaints and causes of chronic abdominal pain. Of 493 boys and 469 girls with a mean age of 9.1 years, 12.7% had been evaluated for chronic abdominal pain. Constipation as cause of abdominal pain occurred in 83%, childhood functional abdominal pain in 8%, colic in 5%, gastroesophageal reflux in 2% and infection in 2%. The life-time prevalence rate for chronic abdominal pain was 13.3%; was due to functional causes in 13.1% and due to organic diseases in 0.2%. Functional constipation was the most frequent cause of chronic abdominal pain in a large primary care paediatric population.