Objective Relationship continuity/discontinuity refers to whether a spouse/partner experiences their current relationship with someone with an acquired brain injury (ABI) as a continuation of their loving pre-injury relationship or as radically changed. The aim of this study was to adapt a questionnaire measure of continuity/discontinuity from dementia research for use in an ABI context and to evaluate the psychometric properties of this adaptation. Method The questionnaire was adapted in response to feedback from a focus group of ABI caregivers. Its psychometric properties were then evaluated in two studies involving partners of people with ABI. Results The measure showed high internal consistency (alpha = .956 in Study 1 and .963 in Study 2), test-retest reliability (intra-class correlation = .960 in Study 1) and discriminative power (Ferguson's delta = .975 in Study 1 and .963 in Study 2). Evidence of construct validity was provided by a predicted pattern of correlations with other relationship questionnaires. Exploratory factor analysis suggested that the questionnaire is unidimensional. Discussion A valid and reliable quantitative measure of relationship continuity/discontinuity will enable more robust evaluation of suggestions about this construct that have been made in qualitative studies (e.g. that discontinuity is associated with a greater sense of caregiver burden).