Poor adherence frequently impaired the efficacy of therapy to maintain remission from inflammatory bowel diseases (IBD). There is a lack of practical and effective interventions to improve adherence. This study aimed to identify modifiable risk factors, which may yield targets for new interventions. Participants with IBD were recruited from hospital outpatient clinics and office-based gastroenterologists. Demographic and disease-related data were recorded by means of self-administered questionnaires. Modifiable risk factors were assessed with the validated Belief about Medicine Questionnaire, Hospital Anxiety and Depression Score, and short inflammatory bowel disease questionnaire. Adherence was assessed separately for 5-aminosalicylates, thiopurines, and biological agents using the validated Medicine Adherence Report Scale (good adherence defined as >16). Nonadherence occurred in 102 of 356 participants (28.7%). Adherence increased significantly with more aggressive therapies (median Medicine Adherence Report Scale: 5-aminosalicylates 18, thiopurines 19, biological 20; P < 0.0001). Nonadherence was not associated with anxiety and depression or disease-related patient knowledge. Adherent patients had significantly higher belief of necessity for medication (P < 0.0001) and a trend toward lower concerns about medication (P = 0.08). Membership of an IBD patient organization was associated with better adherence (P < 0.0001). Concerns about medication rose significantly with more aggressive therapies (P = 0.009), but belief of necessity was similar for all medications. Nonadherence occurs most frequently with 5-aminosalicylates. Belief of necessity may prove the key target for future interventions, although general IBD education is unlikely to yield an adherence benefit. Patient organization membership should be encouraged.