PurposeThe purpose of this study is to investigate the links between lean, service quality expectation (SQE) and service quality performance (SQP) in outpatient departments (OPD).Design/methodology/approachThe measurement instruments were developed from a comprehensive literature review, then verified by experts and confirmatory factor analysis. Multiple responses were applied to improve the reliability of data obtained from 220 Thai hospitals. The hypotheses were tested with linear regression and path analysis of structural equation modeling.FindingsIt was found that lean has significant positive impacts on all SQP dimensions (i.e. tangibility, reliability, responsiveness, assurance and empathy) and on overall SQP. SQE has significant positive direct effects on lean and SQP, and has a significant positive indirect effect on SQP through lean.Originality/valueThis is one of the first examples of research to present insights into the relationships between lean, SQE and SQP in OPD.