Purpose: This paper reports on issues in the development of a measure of the consumer-case worker working relationship in Assertive Community Treatment (ACT). It focuses on an application of the Rasch measurement model in conceptualizing and constructing a measure of the strength of the working between consumers and case workers in ACT. Particular emphasis is given to the contribution of Rasch analysis to developing a conceptualization of the working relationship construct beyond what can be obtained from traditional factor analytic approaches. Design: Scale development procedures included a preliminary conceptualization of the working relationship and development of a test item pool based on a review of the literature, field observations, and focus groups and individual interviews. After review and piloting, a final item pool (n = 83) was field tested in an opportunistic sample. Sample: 219 consumers from 15 ACT teams providing services within metropolitan Chicago participated in the field test. Analyses: An exploratory factor analysis was conducted in order to identify dimensional structures in the data. Analyses were then conducted using the Rasch measurement model to examine the dimensions in the data and estimate the intensity of the underlying construct expressed by each item. Findings: Factor analysis and Rasch analysis yielded similar factor structures and indicated the presence of distinct positive and negative dimensions. Two relationship scales were thus derived. The Rasch estimates established each item's intensity along the underlying dimension. Descriptions of characteristics at different intensities in the positive and negative working relationship variables emerge. Implications: Descriptors defining the relationship continuum provide greater conceptual understanding of the consumer-case worker relationship in ACT. Such understanding may inform practices that can facilitate productive working relationships.