OBJECTIVES:  To validate the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire – C30 (EORTC QLQ-C30) in an Indonesian version. The standard procedure of forward-backward translation was adhered to in the translation procedures, pilot testing, review, and reliability and construct validity evaluation.  METHODS: Data were collected from cancer patients in the Oncology Department of Dr. Sardjito Hospital, Yogyakarta, Indonesia, who were treated with a cisplatin at the dosage ≥ 50 mg/m 2 as monotherapy or in combinations. We used the Short Form-36 (SF-36) to assess the construct validity of our translated questionnaire. RESULTS:  About 85% patients (n=17) were able to fill out the questionnaires by themselves and there were no missing responses to the questions in the pilot study. One hundred twenty-eight patients with different cancer diagnoses were recruited in the validation process from March 2009 to November 2009. The internal consistency was above 0.70 for the SF-36 scales physical function, social function, pain, physical role and emotional role; values > 0.70 were observed in the Indonesian version of EORTC QLQ-C30 scales. Floor and ceiling effects were seen more evidently in the physical, social dimensions, pain and fatigue than in single items. Both of the questionnaires showed that different diagnoses were associated with a similar impact of quality of life in sensitivity tests.  Correlations between Indonesian version of EORTC QLQ-C30 and SF-36 dimensions were moderate: between 0.18 and 0.48 for the five domains. The discriminant validity between the two questionnaires was acceptable (between 0.02-0.47). CONCLUSIONS:  The Indonesian version of the EORTC QLQ C-30 can be used as a questionnaire to assess quality of life in Indonesian cancer patients.