The Functional Interference Estimate (FIE) is a brief, 5-item self-report measure that assesses the degree to which pain interferes with daily functioning. While the FIE has demonstrated reliability and validity with a small normative sample, not much is known about its reliability and validity with a broad sample of individuals with pain. The current study presents FIE score means, variability estimates, reliability and validity data based on a large sample (n = 1,337) of primary care patients who report problematic pain. The FIE has excellent internal consistency and appears to have strong convergent validity with other well-established measures of function (e.g., SF-36 and Dartmouth COOP Charts). Because of its brevity and flexibility, the FIE may be a useful self-report measure of pain functional interference in clinical research on pain.