Introduction Multimorbidity (MM) refers to the coexistence of two or more chronic conditions within one person, where no one condition is considered primary. As populations age and healthcare provision improves, MM is becoming increasingly common and poses a challenge to the single morbidity approach to illness management, usually adopted by healthcare systems. Indeed, recent research has shown that 66.2% of the people in primary care in Ireland are living with MM. Healthcare usage and cost is significantly associated with MM, and additional chronic conditions lead to exponential increases in service usage and financial costs, and decreases in physical and mental well-being. Certain conditions, for example, chronic pain, are highly correlated with MM. This study aims to assess the extent, profile, impact and cost of MM among Irish adults with chronic pain.Methods and analysis Using cluster sampling, participants aged 18years and over will be recruited from Irish pain clinics and provided an information package and questionnaire asking them to participate in our study at three time points, 1year apart. The questionnaire will include our specially developed checklist to assess the prevalence and impact of MM, along with validated measures of quality of life, pain, depression and anxiety, and illness perception. Economic data will also be collected, including direct and indirect costs.Ethics and dissemination Ethical approval has been granted by the Research Ethics Committee of the National University of Ireland, Galway. Dissemination of results will be via journal articles and conference presentations.