The purpose of this study was to validate the Taiwanese version of the M. D. Anderson Symptom Inventory (MDASI-T) in a sample of 556 Taiwanese patients with multiple diagnoses of cancer. The internal consistency Cronbach alpha was 0.89 for symptom severity items and 0.94 for interference items. The test-retest reliability was 0.97 for the severity composite score and 0.96 for the interference composite score over a 3-day interval in a sample of 12 patients. Construct validity was established by factor analysis, which revealed a two-factor structure. Concurrent validity was examined by correlating the MADSI-T scores and scores of the Medical Outcome Study 36-Item Short-Form Health Survey. Known-group validity was established by comparing MDASI-T scores between patients having low functional status and those having high functional status (Karnofsky Performance Status scores<or=50 or >50, respectively) and between inpatients and outpatients. The MDASI-T's sensitivity (its ability to detect small differences in reporting variations) was examined by comparing the MDASI-T composite symptom scores and composite interference scores before, during, and one week after treatment in a sample of 20 breast cancer patients receiving chemotherapy. The MDASI-T is a reliable, valid, and sensitive instrument for measuring the severity and interference with daily life of cancer-related symptoms among Taiwanese cancer patients.