Despite the fact that research has demonstrated consistent associations between self-rated measures of personality dimensions and mental disorders, little has been undertaken to investigate the relation between psychiatric symptoms and response patterns to self-rated tests. The aim of this study was to investigate the association between psychiatric symptoms and response quality using indices from our functional method. A sample of 1,784 participants from a Swiss population-based cohort completed a personality inventory (NEO-FFI) and a symptom checklist of 90 items (SCL-90-R). Different indices of response quality were calculated based on the responses given to the NEO-FFI. Associations among the responses to indices of response quality, sociodemographic characteristics and the SCL-90-R dimensions were then established. Psychiatric symptoms were associated with several important differences in response quality, questioning subjects' ability to provide valid information using self-rated instruments. As suggested by authors, psychiatric symptoms seem associated with differences in personality scores. Nonetheless, our study shows that symptoms are also related to differences in terms of response patterns as sources of differences in personality scores. This could constitute a bias for clinical assessment. Future studies could still determine whether certain subpopulations of subjects are more unable to provide valid information to self-rated questionnaires than others.