National survey data (NCOA/Harris and Associates, 1974) are analyzed in a causal model to discern differences in the effects of widowhood on the well-being of older men and women. Based on previous research on mental illness, mortality differentials, and the quality of life, it is hypothesized that widowhood has an adverse impact on well-being, and that this relation is stronger for men than women. While the data support an overall decline in well-being of persons who are widowed, a direct effect of widowhood is substantial only for the negative dimension of the well-being of women. Widowed persons experience lower levels of well-being largely because they tend to be older, in poorer health, and less active in social life than their married counterparts. In the case of widowed women, low economic resources is also a key factor. A consistent pattern of greater reductions in levels of social participation in widowhood for men was not evident.