Brief symptom instruments are designed to assess symptoms while maintaining low respondent burden, but they may omit important information. Our objective was to determine whether a representative brief symptom instrument effectively captures the full symptom experience of older adults with advanced diseases. In this cross-sectional study, we interviewed 90 community-dwelling adults with cancer, congestive heart failure, or chronic obstructive pulmonary disease regarding the presence of symptoms in the prior 24 hours. Participants rated the intensity and bothersome nature of 15 symptoms--10 symptoms were included in the Edmonton Symptom Assessment Scale (ESAS) plus 5 supplemental symptoms. Participants reported similar proportions of ESAS and supplemental symptoms. Intensity and "bothersomeness" ratings frequently differed. Brief symptom instruments only provide a limited assessment of the respondent's symptom experience. The benefit obtained from incorporating both the intensity and bothersome nature of a longer list of symptoms may outweigh the potential increase in respondent burden.