PURPOSE: To study persistence with inhaled corticosteroids (ICS) and its determinants in asthma-patients. METHODS: From the PHARMO database, asthma-patients (age < 35 years) with a first dispensing for ICS in 1999-2002 and >/= 2 dispensings in theirst year were included. Persistence during the first year was defined as the number of days from start to time of first failure to continue renewal of the initial ICS. Potential determinants of persistence were assessed at ICS-start and 1 year before. RESULTS: The study-cohort included 5563 new users of single ICS and 297 of fixed-combined ICS. Less than 10% of patients using single ICS and 15% of patients using fixed-combined ICS were persistent at 1 year. Similar persistence-rates were observed whenstratified for age (children/adolescents: 0-18 years and adults: 19-34 years). Increased persistence with single ICS was observed with the type of ICS (budesonide), prescriber (specialist), prior use of long-acting beta-agonists, previous hospitalizationfor asthma, metered-dose inhaler, low starting-dose and once-daily dosing regimen at start. Persistence with fixed combined ICS-treatment increased with younger age and was decreased in patients having high starting-dose of ICS and prior use of antibiotics. CONCLUSION: New users of both single and fixed combined ICS have alarming low persistence rates with ICS-treatment in the first year of follow-up. Persistence was mainly related to patient factors, such as severity of disease, and to treatment-related factors, such as once-daily dosing frequency. Copyright (c) 2008 John Wiley & Sons, Ltd.