Diabulimia is a contested eating disorder characterised by the deliberate restriction of insulin by people with type 1 diabetes in order to lose and control their body weight. This article reports the first discourse-based study of diabulimia. It employs a combination of quantitative and qualitative techniques afforded by corpus linguistics, a methodology for examining extensive collections of digitised language data, to interrogate the discourse surrounding diabulimia in an approx. 120,000-word collection of messages posted to three English-speaking online diabetes support groups. The analysis shows how, despite lacking official disease status, diabulimia was nonetheless linguistically constructed by the support group contributors as if it were a medically-legitimate mental illness. This article explores some of the consequences that such medicalising conceptions are likely to have for people experiencing diabulimia, as well as their implications for health professionals caring for people presenting with this emerging health concern in the future.