This paper extends the self-categorisation model of symptom appraisals to predict that individuals who believe they have a given illness will perceive concurrent symptoms relevant to that illness to be more severe when they categorise themselves as members of a group of people with that illness. These predictions are supported with opportunity samples of individuals reporting, or not reporting a common cold (Study 1, N ¼ 60) and reporting colds or tinnitus (Study 2, N ¼ 64). In both studies, relevant symptoms were rated as more severe when illness group memberships were salient. The methodological, theoretical and clinical implications of these findings and possible therapeutic applications of self-categorisation theory (SCT) to symptom perceptions are discussed.