Objective The objective of this study was to investigate the relationship between cost and quality within the health care sector and to establish which factors could influence this relationship. The aim was to investigate the dynamics of the relationship, in order to improve the quality whilst reducing the cost. Design This is a retrospective cohort study, analysing quality, safety, and financial data from a 5‐year period. Setting A publicly funded tertiary hospital. Participants The dependent variable was cost saved, and the independent variables were patient safety, patient satisfaction, and clinical efficiency. Main outcome measures: Financial savings and quality domains. Results A statistically significant relationship between the variables was found. Multivariate analysis derived the equation Y = βX1 + c, where Y is the cost saved, β is the beta coefficient, X1 is the clinical efficiency, and c is a constant. R2 = 0.874 (coefficient of determination), which suggested that the cost saved by the unit varied due to clinical efficiency. Clinical efficiency accounted for 87.4% of the variation in the cost saved by the unit. Conclusions The results indicated that, after the trade‐off value, an improvement in the quality would result in reduced costs for the unit. Clinical efficiency of the services was found to be the key factor determining this relationship. Therefore, strategies to increase clinical efficiency, and thus overall quality, above the trade‐off level could result in significant financial savings. Patient safety and patient experience were positively correlated with clinical efficiency.