This paper presents the validation of a questionnaire to assess user perceptions of an emergency department. The study also includes the analysis of social non-modifiable variables in order to assess whether the perceived quality is affected by them. The sample consisted of 860 subject users Emergency Health Service of Murcia during the years 2008 and 2009. The exploratory factor analysis revealed three factors: Professional competence (a= .92), Organization (a= .60) and Infrastructure (a= .63). Factor scores correlated positively with overall patients’ satisfaction scores. The lineal regression analysis confirms the relevance of these factors to predict satisfaction. No significant differences by gender and educational level were detected in Professional Competence. The Infrastructure assessment is influenced by sex and Organization for both variables. The questionnaire has proven its utility for detecting areas of improvement and for planning intervention strategies in the areas of organization and infrastructure.