Guidance in the UK requires the co-ordination and standardisation of services to protect adults from abuse. However, there remains considerable ambiguity about the basic concepts of abuse and vulnerability. This paper reports an empirical study of factors in professional decision making in relation to identifying and reporting abuse of older people. A systematic review and a panel of expert practitioners were used to identify factors that might influence professional recognition and reporting of elder abuse. These factors were incorporated into a questionnaire that included randomised factorial survey vignettes and additional questions on decision making. Sets of unique vignettes were completed by 190 social workers, nurses and other professional care managers across Northern Ireland in 2008, giving 2,261 randomised vignettes used as the units of analysis. Recognition and reporting were influenced by case factors specific to the abuse event while contextual factors did not significantly influence recognition or referring of abuse. This study has shown that the factorial survey can be a powerful tool to investigate professional decision making. It provides an insight into practitioners' responses to complex ethical dilemmas. The findings are considered within the context of current policy and the need for further research is discussed.