This paper outlines the development of a Caregiver Strain Index (CSI) with a sample of spouses, family, friends, and neighbors, aged 22 to 83, who provided varying degrees of care to recently hospitalized hip surgery and heart patients aged 65 and over. Internal consistency (Cronbach's alpha) for the 13-item CSI on 81 cases was .86. Evidence of construct validity was obtained in three areas: ex-patient characteristics; subjective perceptions of the care-taking relationship by caregivers; and emotional health of caregivers. These results indicate that the CSI is a brief, easily administered instrument which identified strain within our sample of informal care providers. Further development of the CSI is being undertaken for predicting specific caregiver populations at risk. This simple index might be usefully included in any interview or assessment package that examines intergenerational relations involving dependency and care.