Empirical literature examining the emotional lives of adults with severe and profound mental retardation is limited. One area to have received attention is mood. It is proposed that the utility of assessment of mood extends beyond psychiatric diagnosis to issues such as the appraisal of quality of life for individuals with limited or no expressive language. Two themes related to the assessment of mood are evident in contemporary literature. First, attempts have been made to clarify presentation of affective disorders, especially depression, and to improve assessment of depressive symptomatology in adults with mental retardation. A review of current methods for assessing depression indicates significant problems with reliability and validity. There is a need to develop appropriate assessment methods for use in relation to adults with severe and profound mental retardation who are unable to self-report and behavioral methodology might be useful in this respect. Second, there is an emerging argument that presentation of depression in adults with mental retardation, particularly in individuals with severe disabilities, includes challenging behaviors, referred to as "atypical symptoms." Methodological and conceptual issues related to this argument warrant closer examination. Finally, it is noted that research drawing on more rigorous methodology is required to interpret the emotional states of individuals with severe and profound mental retardation.