The completeness of cancer registry data -- the extent to which all of the incident cancers occurring in the population are included in the registry database -- is an extremely important attribute of a cancer registry. Only a high degree of completeness in case-finding procedures will ensure cancer incidence rates and survival proportions are close to their true value. This second instalment of a two-part review of data quality methods at the cancer registry, focuses on the principles and techniques available for estimating completeness, separating methods into those that are semi-quantitative -- in that they give an indication of the degree of completeness relative to other registries or over time, and more quantitative techniques -- those that provide a numerical evaluation of the extent to which all eligible cases have been registered.