We investigated the extent to which methodological concerns explicitly addressed by the designers of the World Mental Health Surveys persist in the results that were obtained using the WMH-CIDI instrument. We compared rates of endorsement of mental illness symptoms in the United States (very high) and Nepal (very low) as they were affected by respondent understanding of the survey, social desirability bias, interview social context and translation-related sources of misunderstanding. The results showed that, although levels of misunderstanding and social desirability were higher in Nepal than in the U.S., these potential methodological concerns had less effect on symptom endorsement in Nepal than in the U.S. In Nepal non-methodological factors related to the socio-cultural context probably had a more substantial impact on observed symptom rates than did the methodological factors. The larger issue is the effect that methodological factors have on the validity of reported rates of disorder.