Health practitioners often regard complaints about the quality of patient care in a negative light. However, complaints can indicate strategies to improve care. Therefore, an audit was undertaken of all formal complaints about patient care at a major Australian hospital over a 30-month period. The profile of complainants, the reasons for complaints, and the outcome were analysed. A total of 1308 complaints, concerning the care of 1267 patients, were received. The complaint rate was 1.12 per 1000 occasions of service. In all, 57% of complaints were lodged by advocates and 71% of complaints related to poor communication or to the treatment provided. In 97% of occasions, an explanation and/or an apology resulted. To date, no complaint has proceeded to litigation. Complaints are potentially useful quality assurance tools and can identify remediable system flaws. Health professionals and employers should understand why patients complain and be able to respond appropriately.