BACKGROUND AND PURPOSE - Stroke symptoms in the absence of recognized stroke are common, but potential associated dysfunctions have not been described. METHODS - We assessed quality-of-life measures using the Physical and Mental Component Summary scores of the Short Form 12 (PCS-12 and MCS-12) in the REasons for Geographic And Racial Differences in Stroke (REGARDS) cohort. Differences in mean PCS-12 and MCS-12 scores were assessed among participant groups symptoms-free (n=16 090); history of stroke symptoms but free of stroke/transient ischemic attack (n=3404); history of stroke (n=1491); and history of transient ischemic attack (n=818). RESULTS - Participants with symptoms (but no diagnosis) had average PCS-12 scores 5.5 (95% CI: 5.2 to 5.9) points lower than those without symptoms, a difference similar to transient ischemic attack (6.0; 95% CI: 5.3 to 6.7) and over one half the effect of stroke (8.4; 95% CI: 8.0 to 9.0). MCS-12 scores were 2.7 (95% CI: 2.4 to 3.0) points lower for those with symptoms, -0.5 for transient ischemic attack (95% CI: 0.0 to -1.1), and -1.6 for stroke (95% CI: -1.2 to -2.0). Differences in demographic and vascular risk factors, health behaviors, physiological measures, and indices of socioeconomic status did not fully explain these differences. Those reporting history of weakness or numbness had larger current decrements in physical functioning, and those reporting history of inability to express themselves or understand language had larger current decrements in mental functioning. CONCLUSIONS - Individuals with clinically consistent symptoms but no stroke diagnosis have a lower quality of life than those without symptoms. The difference in physical functioning is substantial with a smaller decline in mental functioning. Apart from so-called "silent stroke," there appear to be many individuals with possibly symptomatic cerebrovascular disease-either stroke or transient ischemic attack-who are not being diagnosed. Furthermore, these symptomatic but undiagnosed strokes may not be benign. © 2007 American Heart Association, Inc.