Most research on illness representations explores how patients view single conditions, but many patients report more than one long-term condition (known as multimorbidity). It is not known how multimorbidity impacts on patient illness representations. This exploratory qualitative study examined patients' representations of multimorbid long-term conditions and sought to assess how models of illness representation might need modification in the presence of multimorbidity. We explored two major issues: (1) the impact of multimorbidity on patient representations of their individual conditions and (2) the representation of multimorbidity itself. Twenty eight adults with at least two long-term conditions (mean of 4) were interviewed. The presence of multimorbidity impacted on patient illness representations in relation to the dimensions of identity, perceived cause, coherence and consequences. Representations of multimorbidity itself concerned representations of the burden of medication and perceived priorities among conditions and synergies and antagonisms between conditions and their management. The results have implications for the measurement of multimorbidity (through scales such as the Illness Perception Questionnaire) and the use of illness representations in the design and delivery of interventions to improve health behaviour and outcomes of patients with multiple long-term conditions.