How is genetic involvement interpreted for disorders whose medicalisation is contested? Framing psychiatric and behavioural disorders in terms of genetics is expected to make them seem more medical. Yet a genetic aetiology can also be used to frame behaviour as acceptable human variation, rather than a medical problem (for example, sexual orientation). I analyse responses to the idea that there is a genetic component in anorexia and bulimia nervosa (AN or BN) via semi-structured interviews with a sample of 50 women diagnosed with an eating disorder (25 had recovered). All but three volunteered that genetics would medicalise AN or BN by (i) making eating disorders seem more like ‘real diseases’; implying that these disorders need (ii) professional treatment or (iii) a biologically based treatment. The results also indicate there are several counter-logics by which genetic framing could support non-medical definitions of AN or BN. I argue that genetic framing reduces perceived individual responsibility, which can support definitions of behaviour as either a reflection of disease (which entails intervention) or a reflection of normal human diversity (which does not). In the context of public scepticism as to the ‘reality’ of AN or BN, genetic involvement was taken as evidence of disease in ongoing negotiations about the medical and moral status of people with eating disorders.