Background: insight into co-morbidity and treatment effects is pivotal to improve quality of care for cancer patients. Objectives: To determine whether linkage of the Eindhoven Cancer Registry (ECR) and the PHARMO Record Linkage System (RLS) was technically feasible and to assess which patient-centric data would result from this linkage. Methods: The ECR records data on tumour stage and primary treatment of all newly diagnosed cancer patients in the southeastern Netherlands including co-morbidity at diagnosis, whereas the PHARMO RLS includes data from multiple linked observational databases such as data on drug utilisation (for both in- and out-patients, including chemotherapy), hospitalisations and clinical laboratory measurements. All patients who lived or had been living in the overlapping area served by the ECR and the PHARMO RLS during 1998-2006 were selected for linkage which was performed with probabilistic medical record linkage. Results: The linkage resulted in an ECR-PHARMO cohort of 40,004 cancer patients with a total of 42,767 primary tumours. The cancer patients in the linked ECR-PHARMO cohort were representatives for the cancer patients included in the total ECR during 1998-2006. Cancer patients included in the cohorts had a mean history of 5 years and a mean follow-up ranging from 2 to more than 4 years (dependent on the survival rate of the specific cancer type). Conclusions: Linkage of ECR and the PHARMO RLS creates the possibility to study patient-centric drug utilisation, health resources utilisation and their costs, in addition to the effectiveness and safety of pharmaceuticals in routine daily practice in cancer patients. (C) 2009 Elsevier Ltd. All rights reserved.