Today, many countries are increasing their efforts to ensure that all cancer patients receive the best possible care. Population-based cancer registries have adapted their registration to collect additional clinical variables to provide clinicians with unbiased population data on cancer treatment and survival. Taking several examples of epidemiological cancer research performed at the Geneva Cancer Registry, we aim to illustrate how cancer registries oversee the treatment and outcomes of cancer patients to help clinicians continually improve quality of care and prevent cancer deaths in the population.