This report introduces the framework, subject matter, methods, study designs, and problems in the assessment of quality of clinical care. So far, many population-based cancer registries do not have much experience in this field. Thus, potential data sources are described and practical examples of successful studies are given to encourage further work and studies, especially international collaborations. The publication is aimed at cancer registry staff, clinical epidemiologists and auditors, and health care planners, as well as clinicians with special interest in collaborating with population-based cancer registries.