Syndemic theory is described as population-level clustering or co-occurrence of health conditions in the context of shared aetiologies that interact and can act synergistically. These influences appear to act within specific places of high disadvantage. We suggest ethnic inequality in experiences and outcomes of multimorbidity, including psychosis, may be explained through a syndemic framework. We discuss the evidence for each component of syndemic theory in relation to psychosis, using psychosis and diabetes as an exemplar. Following this, we discuss the practical and theoretical adaptations to syndemic theory in order to apply it to psychosis, ethnic inequality and multimorbidity, with implications for research, policy, and practice.