The WHOQOL is a new measure designed to assess quality of life cross-culturally in health and health care. An international core of 276 items covering 29 facets of quality of life organised into 6 domains has been established conceptually and then assessed in psychometric terms. The method also allowed for the inclusion of extra national items to enable the concept of quality of life to be complete for each language and culture and to achieve conceptual equivalence between different language versions in participating centres. The present study investigates the properties of these national items using data obtained from 3740 participants world-wide, who completed the instrument in 10 of 16 original WHOQOL centres. Five statistical criteria were applied to 144 national items to examine their performance in competition with internationally agreed core items from the same facet, using data obtained from within that centre. Multi-dimensional scaling and cluster analysis was used to examine the structural relationship of national items within their own facet and directed their inclusion. Forty (29%) national items were selected and detailed examples demonstrate the selection methods used. They show how entirely new facets as well as individual items can be assessed for appending to the core WHOQOL-100. They also enable ambiguity to be resolved where there may be doubt about whether proposed items constitute part of an existing facet or justify a new one. Where national items are similar in more than one centre, a mechanism is provided whereby these items can be re-evaluated as candidates for inclusion in any future revision of the international core. Lastly, a case is identified that may provide justification for the establishment of national facets.