This study aims to investigate the nature and resolutions of patient complaints and further to explore the use of complaints to drive quality improvement in a selected hospital in Taiwan. A teaching hospital (i.e. the Case Hospital) in Taiwan was purposefully chosen for a case study. The author conducted the critical incident technique (CIT) using questionnaires to obtain information about the complaints and the process of their resolutions. To enhance the reliability of the study, the author also conducted non-participant observations as an outsider at the Case Hospital. In this study, 59 complainants registered 87 complaints. The CIT found that care/treatment, humaneness and communication were the most common causes of complaints. The response time of patient complaints averaged 1.76 days, except for five cases in which response time was not reported. The majority of complaints were resolved within three days. Moreover, this study found that of 149 resolutions, 105 taken by the hospital involved an explanation of the facts to complainants (n = 41), investigation of events (n = 33) and empathy with complainants (n = 31). The lack of any systematic use of complaints data was one of the most crucial failures of the Case Hospital. Instead of attempting to use such data as the basis for initiating quality improvement measures, complaints were consigned to a 'black hole' where their existence was conveniently forgotten. Based on this study, the author suggests ways to strengthen the capacity of the hospital in terms of using patient feedback and complaints to improve the quality.