The completeness of cancer registration in the IKL (Integraal Kankercentrum Limburg) cancer registry, Limburg, the Netherlands, was evaluated for the years 1988-1990 by means of the independent case ascertainment method. This study was performed in co-operation with the Registration Network of Family Practices (RNFP) of the University of Limburg. The RNFP is a centralized database used by general practitioners (GP), containing their patients' background variables and diagnoses. The contents of the two databases were compared using computerized record linkage. If the information from both databases differed, this was verified using the source forms of the cancer registry and the GP involved. By combining the information from both registries in this way it was determined which malignancies should have been registered by the cancer registry. The IKL cancer registry had recorded 307 of the 319 eligible malignancies (96.2%). Five of the 12 missed registrations could be attributed to systematic shortcomings in the notification procedures. The estimated completeness for all malignancies of the IKL cancer registry is comparable with the results from cancer registries outside the Netherlands which have been established for longer.