Addressing the characterization of social and economic determinants of health (SDH) properly is a key aspect in conducting a Health Impact Assessment (HIA). This article explores the level of knowledge on HIA environmental and public health professionals have as well as their perception regarding key concepts such as the definition of ‘health’ and the relevance of SDH. With this purpose in mind, a survey was conducted among experts (n = 41) who attended a technical session on HIA within the framework of the most important conference on the Environment on a national level in Spain. A hierarchical cluster analysis was conducted to categorize groups of respondents depending on their working profile and professional expertise and a Friedman test was used to compare mean ranks so as to assess the importance given to SDH according to the target respondents’ perception. Strong differences were found in the relevance given to diverse SDH according to their contribution to a good state of health, the block referring to ‘Habits and lifestyle’ being the one perceived as more significant. SDH were ranked in a diverging order from that reported in the scientific evidence regarding the association between SDH and a wide range of health outcomes. Also, some diverging trends were illustrated between groups of respondents according to the relevance given to each block of SDH. However, differences in responses between groups of respondents were not statistically significant. A self-appraisal by respondents also revealed that the practitioner’s level of knowledge on HIA ranged between low to medium. Therefore, it is recommended to improve their capacity.