Effective assessment and management of pain in patients with cancer is strengthened by the patient's report of how much pain interferes with daily functioning. This requires a clear delineation of different levels of pain interference. We derived optimal cutpoints for differentiating between mild, moderate, and severe pain interference assessed by the Brief Pain Inventory (BPI) and describe the prevalence and characteristics of pain-induced functional impairment in patients with cancer. Data were pooled across 3 Phase III pivotal trials. Patient-completed questionnaires included the EuroQol 5 dimensions questionnaire (EQ5D), Functional Assessment of Cancer Therapy-General Measure (FACT-G), and BPI. Optimal cutpoints for categorizing pain interference into 3 levels were derived using analysis of variance, with different cutpoint sets for BPI total interference (BPI-PITS, the average score of all 7 items), activity-related interference (BPI-WAW, the average score of work, general activity, and walking), and mood-related interference (BPI-REM, the average score of relations with others, enjoyment of life, and mood) as independent variables and EQ5D-visual analog scale and total FACT-G score as dependent variables. To validate the cutpoints, we assessed whether interference categories were in concordance with Eastern Cooperative Oncology Group performance status (ECOG-PS) levels. The optimal cutpoints were (2,5) for BPI-PITS, (2,6) for BPI-WAW, and (2,5) for BPI-REM. The mild (<2), moderate (2-5 or 2-6), and severe (>5 or >6) pain interference groups were significantly concordant with ECOG-PS levels (P < 0.0001). We empirically derived patient-reported pain interference categories in relation to clinician-rated performance status. These cutpoints may facilitate the conduct and interpretation of clinical evaluation, symptom epidemiology, and clinical trials.