OBJECTIVE: Nonadherence to regular inhaled anti-inflammatory medication use is a frequent contributor to poor control of persistent asthma and may result from misunderstanding of the preventive role of such medications. This study’s aims are to 1) test the hypothesis that misunderstanding is associated with decreased adherence to its daily use and 2) identify factors associated with increased risk of misunderstanding. STUDY DESIGN: A sample of parents of children with asthma insured by Medicaid and enrolled in managed care programs in Northern California, Washington, and Massachusetts were interviewed by telephone. This analysis focused on the subset that reported having an inhaled anti-inflammatory medication and whose medication use and symptom frequency in the 2 weeks before the interview suggested persistent asthma. Misunderstanding of the role of inhaled anti-inflammatory medication was defined as identifying it as being for treatment of symptoms after they begin and not for prevention of symptoms before they start. RESULTS: A total of 1663 parents of children with asthma (63% response rate) were interviewed. Of those, 571 subjects (34%) reported use of an inhaled anti-inflammatory medication and met our criteria for persistent asthma. Among those with persistent asthma, 23% (131 parents) misunderstood the role of their child’s inhaled anti-inflammatory. Misunderstanding of inhaled anti-inflammatory medication was associated with decreased adherence to its daily use (odds ratio [OR] 0.18, 95% confidence interval [CI], 0.11-0.29). The risk for misunderstanding was lower if the patient had seen a specialist (OR 0.42, 95% CI, 0.24-0.75) or had graduated high school (OR=0.54, 95% CI, 0.34-0.84). CONCLUSION: Misunderstanding of the role of inhaled anti-inflammatory medication is associated with reduced adherence to its daily use.