Many patients consulting in primary care have multiple conditions (multimorbidity). The aims of this review were to identify measures of multimorbidity and morbidity burden suitable for use in research in primary care and community populations, and to investigate their validity in relation to anticipated associations with patient characteristics, process measures and health outcomes. We included 194 papers describing 17 different measures. Different measures appeared to be most appropriate according to the outcome of interest and the choice of measure will partly depend on the type of data available. Comparative studies demonstrated few differences in the predictive validity of different measures but more research is needed to directly compare the performance of different measures.