OBJECTIVE: To assess the validity and reliability of EORTC QLQ-C30 in patients with cancer in Singapore. METHODS: A total of 62 patients at Cancer Center of National University Hospital were asked to complete independently QLQ-C30 and a generic questionnaire (SF-36). The sociodemographic data were obtained simultaneously. RESULTS: The QLQ-C30 demonstrated good internal reliability for most scales with Cronbach's alpha more than 0.7 except cognitive functioning, physical functioning, and nausea and vomiting scale. The majority of item-scale Pearson's coefficients (corrected for overlap) were more than 0.4 and higher as opposed to that between the item and competing scales in the same instrument. All functioning scales in QLQ-C30 had strong correlations with the scales measuring the similar aspect of QoL in SF-36. The correlation coefficients among all scales were significant but modest (ranging from an absolute value of 0.23 to 0.65). CONCLUSION: In our study, QLQ-C30 could be considered reliable and valid using to evaluate health related quality of life (HRQoL) in cancer patients in Singapore.