Purpose The purpose of this paper is to present an approach based on the thinking process of the theory of constraints (TP–TOC) to support decision-makers, managers and professionals of health to diagnose and improve healthcare systems focusing on the service quality deployed to patients. Design/methodology/approach A case study was developed in a SUS-affiliated philanthropic hospital in southern Brazil, through the analysis of its ED processes and application of the TP–TOC. The Current Reality Tree and the Evaporating Cloud tools of the TOC were used to identify the root causes (RC) and their connections with undesirable effects. Findings The analysis of this case helped to understand and identify the causes of the current problems in the analyzed processes related to internal management and external causes. The proposed approach allowed the hospital team to progress in the understanding of such causes in a sequential manner, giving conditions to apport different perceptions and to identify relevant facets and causes related to the problem. The research provided a systemic and an integrated vision of the losses in the organizational processes and indicated the steps to be prioritized in order to eliminate such losses. Originality/value The paper proposed an approach that allowed the systematic and systemic analysis of organizational processes through the application of the TP–TOC. The recognition of the existence of RC responsible for processes losses represents an excellent opportunity for improvement because it allows managers to focus their efforts on the more productive areas.