The purpose of this study was to validate the core EORTC quality of life questionnaire, the QLQ-C30 (version 3.0), for use among Turkish and Moroccan cancer patients in the Netherlands. The questionnaire was translated into two oral Moroccan languages, and the existing Turkish version was culturally adapted for use in the Netherlands. Ninety Turkish and 79 Moroccan patients completed the questionnaire. Administration of the questionnaire proved feasible, with low levels of missing questionnaires (4%) and missing items (on average, 1.5-2.4%). With one minor exception, the evidence of convergent validity was strong for all multi-item scales. Internal consistency reliability was above 0.70 for all scales except the cognitive functioning scale in the Turkish sample. The questionnaire was able to distinguish clearly between subgroups formed on the basis of performance status and comorbidity, and was moderately responsive to change over time in performance status. These data support the use of the QLQ-C30 among Turkish and Moroccan cancer patients residing in the Netherlands. Additional studies are needed to confirm the psychometrics of the questionnaire when used among these ethnic minority groups residing in other Western European countries.