Cognitive behaviour therapy (CBT) is now suggested to be the treatment of choice for bulimia nervosa. However, it is also known than no more than approximately 50% of patients recover after receiving CBT. When the first-line manual-based treatment fails, the therapist should use other empirically supported treatments, and if they do not work or are not available, then the therapist should resort to the problem-solving (hypothesis-testing) approach that characterises CBT. However, using problem-solving strategies demands a thorough analysis and understanding of the variables maintaining the problems. Behavioural functional analysis, which lies at the core of behaviour therapy and applied behaviour analysis, helps the therapist to gain the understanding needed for using relevant cognitive and behavioural treatment strategies and methods. However, functional analysis has been criticised for lack of replicability and cost-ineffectiveness. Logical functional analysis (LFA) is a recent development that seems to be both replicable and useful for treatment planning. In this paper, an LFA of eating disorders that helps to guide the CBT treatment and makes it more individualised is described, discussed, and illustrated by a case example. (Contains 1 figure.)