Cancer registries are sources of epidemiological, patterns‐of‐care, and outcome data for local, regional, state, and national studies of patients with cancer. Since 1976, these registries have formed a voluntary network of contributors to annual patient care studies under the aegis of the National Cancer Data Committee of the Commission on Cancer. These annual studies provide timely clinical information that is widely disseminated to physicians, allied health personnel, administrators, health care planners, and public and private agencies. The use of the data has grown exponentially and has been the basis for more than 90 publications. Merging this activity with the National Cancer Data Base has further expanded the demand and use of registry data. This study was undertaken to respond to inquiries as to the validity of the data and the qualifications and competency of cancer registrars. It provides the baseline for cancer registry data quality and serves as a quality management tool to identify opportunities to enhance data quality. © 1995 Wiley‐Liss, Inc.