Longitudinal data from the Alameda County Study are used to examine three health consequences of multiple or co-morbidity, defined as the coexistence of two or more chronic conditions and/or symptoms. Age-adjusted analyses of the consequences of baseline co-morbidity show significant associations in both age groups with 17-year mortality, and with the development of multiple new conditions and the occurrence of depression over a 9-year follow-up. After adjustments for sociodemographic characteristics and health behaviors, all associations with multiple new conditions remain significant. The association with depressive symptoms, however, remains significant for the younger age group only and the association with mortality become nonsignificant in both age groups.