Inner strength is a conceptualization of a human resource that is generally considered beneficial for health and well-being. Previously, it has been examined in qualitative and cross-sectional studies, but longitudinal data are lacking. The aim of this study was to examine how inner strength, health and function, well-being, and negative life events, namely crises and diseases, affect each other over time in old people. A longitudinal two-wave design was used with data from 2010 and 2016. A total of 4023 participants, living in Finland and Sweden, and born in 1930, 1935, 1940, or 1945 were included. Data were collected using the Inner Strength Scale, the Life Orientation Scale, a short version of the Geriatric Depression Scale, one item from the SF36, and five items from the Katz ADL-index. Structural equation modeling was used to test for cross-lagged effects. Crises and diseases were found to be a positive predictor of inner strength, a negative predictor of well-being, and to have no significant effect on health and function over time. Inner strength and well-being had a reciprocal positive relationship, and health and function was a positive predictor inner strength. The study expands findings by providing perspectives of inner strength across time indicating that inner strength in old people increases when they have to face a disease or crisis. From a health perspective, the present findings reinforce the importance of healthcare professionals' awareness and knowledge of the construct of inner strength.