Central cancer registries in North America routinely collect information on the residential address of each person diagnosed with cancer. The residential address at the time the patient was diagnosed with cancer and the current residential address are both collected for differing purposes. The address at time of diagnosis is used by epidemiologists for a variety of purposes, such as cancer cluster investigations and descriptive epidemiological reports to show the geographical distribution of cancer and cancer trends over time. The current residential address is used primarily for patient follow-up activities.