OBJECTIVES The objective of this study was to assess the test-retest reliability of an interactive voice response (IVR) version of the EORTC QLQ-C30. METHODS A convenience sample of outpatient cancer clinic patients (n= 127) was asked to complete the IVR version of the QLQ-C30 twice, two days apart. The QLQ-C30 is a 30-item, cancer-specific questionnaire composed of single-items and multi-item scales. The instrument has five functional scales (physical, role, cognitive, emotional, and social), three symptom scales (fatigue, pain, and emesis), and a global health/quality of life scale. The remaining single items assess dyspnoea, appetite loss, sleep disturbance, constipation, and diarrhoea. The analyses focused on intraclass correlation coefficients (ICCs), comparing the ICC 95% lower confidence interval with a critical value of 0.70. RESULTS Subjects who did not complete the second assessments within 72 hours or who had score differences on the scales or items exceeding two standard deviations were excluded from the per protocol analyses. The sample sizes used in the per protocol analyses ranged from 112 to 115 subjects. The ICCs for the 9 multi-item scales were all above 0.69, ranging from 0.698 to 0.926 (ICC 95% lower CI range: 0.608 to 0.901). All of the scales were significantly different from our threshold reliability of 0.70, with the exception of the cognitive functioning scale. The ICCs for the 6 single items ranged from 0.782 to 0.908 (ICC 95% lower CI range: 0.714 to 0.876) and all were statistically different from 0.70. The evidence supports the stability of the scores obtained on the IVR version of the QLQ-C30 upon repeated measurement. CONCLUSIONS The equivalence of the IVR and paper versions of the QLQ-C30 has been demonstrated elsewhere. This analysis provides additional evidence of the test-retest reliability of the IVR version of the QLQ-C30.