BACKGROUND There has been a lack of qualitative research specifically in patients with inflammatory bowel disease relating to reasons for failure to take medication. We aimed to address this gap and also identify factors which might increase adherence. METHODS Twenty-seven patients from 3 UK hospital sites (Leicester, Norwich, and Cardiff) were recruited to take part in a qualitative study based on semistructured interviews. RESULTS A model was developed to illustrate the way in which patients appear to balance the benefits and disadvantages of taking 5-aminosalicylic acid (5-ASA) medication. The degree of information held by patients regarding ulcerative colitis (UC) and self-evaluation of the benefits of 5-ASA appears to impact whether patients accept or reject the medication. Decision-making on an ill-informed basis may be a factor leading to a reduction in adherence. Due to the nature of the condition, adherence levels may be affected by potential difficulties in terms of experiencing and understanding the links between the medication and health outcomes. CONCLUSIONS Important determinants of adherence to 5-ASA medication in patients with UC appear to include the level of information provided and patient beliefs about prescribed 5-ASA. Patient adherence to 5-ASA requires encouragement and reinforcement and the patient-clinician relationship has a crucial role to play in this dynamic.