Characteristics of the self-definition were investigated in a heterogeneous sample of 516 participants of the Berlin Aging Study (aged 70-103 yrs). The investigation of the self-definitions of older adults provides insights into the salient life themes and processes of their person-environment interaction. An analysis of the content of the self-definition revealed that old and very old individuals defined themselves as active and present-oriented. At the same time the content of their self-definitions reflected an inward orientation and a central theme of life-review. As expected, health was one of the most important life issues. Although even the very old produced more positive than negative evaluations in their self-definition, the ratio of positive to negative evaluations was less favorable for the 85 to 103 yr olds when compared with the 70-85 yr olds. The multifacetedness of the self-definition appears to decrease in very old age as a function of health-related constraints. Positive emotional well-being was associated with having more self-defining domains and a richer description of these domains. Multifacetedness of the self-definition, however, did not buffer against the negative effect of diminished functional capacity on positive emotional well-being. (PsycINFO Database Record (c) 2007 APA, all rights reserved)