Active follow-up usually means that the registry attempts to contact physi- cians or patients on a regular basis to see if the patient is still alive. Because this is expensive, many registries rely on passive follow-up, matching with death certificates and assuming patients are alive otherwise. Mixed systems use death certificates plus updating the ‘date last known alive’ from hospital admissions, consultations, and other sources of data. Active follow-up of the patients is usually very difficult in developing coun- tries. Few registries have the necessary facilities for regular follow-up of patients. There are also problems with unreliable postal services, unstable addresses and mobility of the population. Passive follow-up is.
