OBJECTIVES: Large, nationally-representative data sources of epidemiological and health outcome information are scarce in Japan. The aim of this study was to assess the evidence for validity of a national patient-reported survey of the adult Japanese population compared with existing population-based studies. METHODS: The data source for this comparison was the 2010 Japan National Health and Wellness Survey (NHWS) (N=25,000). The NHWS is a self-reported, Internet-based survey administered to the adult population of Japan.  A random stratified sampling framework was implemented, with age and gender strata, to ensure the final NHWS sample was identical to the demographic composition of the Japanese population. Sampling weights were applied to all analyses to project to the entire country’s population. Prevalence statistics generated from NHWS were then compared with existing epidemiological information obtained through literature reviews. RESULTS: For certain conditions defined by clinical measures that patients may not be aware of (e.g. COPD), large differences in prevalence between NHWS (COPD = 1.37%) and the literature (10.9% reported airflow limitations in Fukuchi et al., 2004) were observed.  In these cases, differences generally disappeared when analyses focused purely on prevalence of awareness of diagnosis (NHWS 1.37% vs. Fukuchi et al., 2004: 1.02%).  Though some differences were observed, most other conditions were generally similar between NHWS and the literature (e.g., atrial fibrillation: 0.73% vs. 0.56%, respectively; asthma: 2.55% vs. 3.40%, respectively). CONCLUSIONS: Although population-level data in Japan are scarce, patient-reported data can provide useful epidemiological estimates as well as valuable health outcome data across a variety of conditions.  In many instances, NHWS prevalence rates were comparable to other sources though, because the NHWS is purely self-report, it provides a perspective based on awareness of diagnosis, which may not be relevant for all disease. Further comparisons between the NHWS and other population-based studies are warranted.