INTRODUCTION: Multimorbidity is increasingly recognized as a key issue in the prevention and management of chronic diseases. We examined the prevalence and correlates of chronic disease multimorbidity in the general adult Canadian population in relation to age and other key determinants. METHODS: We extracted data from the Canadian Community Health Survey 2011/12 on 105 416 Canadian adults. We analysed the data according to the number of multimorbidities (defined as 2+ or 3+ diseases from a list of 9) and examined the determinants of multimorbidity using regression analyses. RESULTS: Our findings show that 12.9% of Canadians report 2+ chronic diseases and 3.9% report 3+ chronic diseases. Those reporting 3 or more chronic diseases were more likely to be female, older, living in the lowest income quintile and to have not completed high school. In the overall population, social deprivation is associated with a 3.7 odds of multimorbidity, but when examined across age groups, the odds of multimorbidity were notably higher in middle age, 7.5 for those aged 35 to 49 years and 5.4 for those aged 50 to 64 years. DISCUSSION: As the proportion of Canadians living with multiple chronic diseases increases, we need to assess chronic disease from a holistic perspective that captures multimorbidity and upstream factors, to facilitate broader and more context-appropriate associations with healthy living, quality of life, health care costs and mortality. Special consideration should be given to the role that social deprivation plays in the development of multimorbidity. Canadians living in the lowest socioeconomic group are not only more likely to develop multimorbidity, but the onset of multimorbidity is also likely to be significantly earlier.