Health impact assessment (HIA) is a prospective decision-making aid tool that aims to improve the quality of policies, programmes or projects through recommendations that promote health. It identifies howand through which pathways a decision can impact a wide range of health determinants and seeks to define the distribution of effects within populations, thereby raising the issue of equity. HIAwas introduced to the WHO European Healthy Cities Network as one of its four core themes during the Phase IV (2004-08). Here we present an evaluation of the use of HIA during Phase V (2009-13), where HIA was linked with the overarching theme of health and health equity in all local policies and a requirement regarding capacity building. The evaluation was based on 10 case studies contributed by 9 Healthy Cities in five countries (France, Hungary, Italy, Spain and the UK). A Realist Evaluation framework was used to collect and aggregate data obtained through three methods: an HIA factors analysis, a case-study template analysis using Nvivo software and a detailed questionnaire. The main conclusion is that HIA significantly helps promote Health in All Policies (HiAP) and sustainability in Healthy Cities. It is recommended that all Healthy City candidates to Phase VI (2014-18) of the WHO Healthy Cities European Network effectively adopt HIA and HiAP. © The Author 2015. Published by Oxford University Press. All rights reserved.