Attachment theory-guided studies of older adults have generally relied on self-report measures that were validated on young adult samples and that focus on fears of rejection by romantic partners and on experiences of chronic discomfort with romantic intimacy as the key indicators of adult attachment security. These assessment characteristics raise important questions as to whether these measures are appropriate for use with older adults. Unlike their younger adult counterparts, older adults may face distinctive life stage-related threats to their attachment security such as declining health and autonomy, spousal loss, and increased dependence on younger family members for instrumental and emotional support. In response to these concerns, we conducted two independent studies aimed at developing and validating a novel measure of attachment security in older adults—the Late Adulthood Attachment Scale (LAAS). In study one (N = 287), exploratory structural equation modeling (ESEM) methods were used to identify and support a 2-factor structure (Fearful Avoidance, Secure Engagement) underlying LAAS scores. In study two (N = 417), ESEM and regression analyses confirmed the 2-factor structure and demonstrated the ability of LAAS scores to predict participants’ well-being over a 3-month interval (n = 93). Findings from both studies support the psychometric adequacy of the LAAS as an alternative measure of attachment security for use with older adult samples.