OBJECTIVES: Databases contain large numbers of unselected patients with extensive medical and demographic data spanning many years.  Considerable interest exists in using large databases to inform economic modelling.  Accurate linkage and costing are essential to optimising their use in economic evaluation. These methods deliver a template to do this. Patients with Irritable bowel syndrome (IBS) can be diagnosed and managed entirely in primary care yet around 30% are referred to gastroenterology.  We use routinely collected electronic records to assess how this referral changes total healthcare utilization and its cost. METHODS: Within the UK Clinical Practice Research Dataset (CPRD) we identified IBS patients with a first gastroenterology visit identified in linked Hospital Episode Statistics (HES) in 2008/9. Anyone with organic gastrointestinal disease was excluded.  All primary care attendances and prescriptions were identified from CPRD and unit costs attached.  Hospital inpatient stays, outpatient visits and colonoscopies were identified in HES.  Healthcare Resource Grouping (HRG) was done via the UK NHS algorithm and tariff costs applied. Utilization rates and costs (2011/2012 UK £) per person year and ratios before and after gastroenterology visit were calculated and stratified.  RESULTS: In 2008/9, 4811 IBS patients attended gastroenterology for the first time. Healthcare utilization increased in all domains before the year of referral and decreases after, except prescriptions which continue to increase. Mean total annual cost was £2492 three years before referral and £3352 three years after (£807 and £821 respectively excluding prescription costs).  Costs were greatest in older patients, those in lower socioeconomic groups, smokers and those diagnosed with IBS less than a year. CONCLUSIONS: Complete primary and secondary healthcare utilization and costs can accurately be calculated at individual and cohort level using routinely collected data from large databases and tariff prices. These data could be used directly in economic modelling from the payer’s perspective and to inform policy.