Research on stress is multifaceted and undertaken at many levels of analysis. Discipline differences in definition and measurement have contributed to divergent findings. Although there is general agreement that stress plays a role in aging, there is less consensus about the precise nature of the relationship and the mechanisms. Predictions about positive and negative relations between stress and aging depend on the nature, time of exposure, intensity, and chronicity of stress. Findings from the Berlin Aging Study (BASE), a longitudinal study of men and women aged 70-100, are used to illustrate stress-related phenomena observed at the behavioral level in very old age. Health-related stressors become chronic strains in daily life for the majority of older adults. Changes in profiles of psychological functioning (cognition, self-regulation, well-being) suggest a distress syndrome indicative of a gradual breakdown of the psychological system. This breakdown is linked to decreased well-being and mortality.