Objective: The objective of this study was to explore the construct of intolerance of uncertainty in patients with anorexia nervosa through focus groups. Method: Nine women with anorexia nervosa participated in three focus groups in an in-patient, rehabilitation and day care setting. Focus groups probed participants' experiences of uncertainty and the meaning to them of uncertainty on a physical, behavioural, cognitive and emotional level. Results: Data were analysed using Interpretative Phenomenological Analysis (IPA). Patients experienced uncertainty as stressful and wanted to avoid this at all costs. Prominent sources of uncertainty were fear of negative evaluation by others and feelings of being imperfect. Uncertain situations led participants to feel anxious and 'out of control', resulting in a strong desire for control which manifested in extreme organising and planning. Discussion: Results suggest that treatment strategies aimed at increasing tolerance of uncertainty in people with anorexia nervosa could be beneficial. Copyright (C) 2010 John Wiley & Sons, Ltd and Eating Disorders Association.