Background: Case conceptualization is assumed to be an important element in cognitive-behavioural therapy (CBT) because it describes and explains clients’ presentations in ways that inform intervention. However, we do not have a good measure of competence in CBT case conceptualization that can be used to guide training and elucidate mechanisms. Aims: The current study addresses this gap by describing the development and preliminary psychometric properties of the Collaborative Case Conceptualization – Rating Scale (CCC-RS; Padesky et al., 2011). The CCC-RS was developed in accordance with the model posited by Kuyken et al. (2009). Method: Data for this study (N = 40) were derived from a larger trial (Wiles et al., 2013) with adults suffering from resistant depression. Internal consistency and inter-rater reliability were calculated. Further, and as a partial test of the scale's validity, Pearson's correlation coefficients were obtained for scores on the CCC-RS and key scales from the Cognitive Therapy Scale – Revised (CTS-R; Blackburn et al., 2001). Results: The CCC-RS showed excellent internal consistency (α = .94), split-half (.82) and inter-rater reliabilities (ICC =.84). Total scores on the CCC-RS were significantly correlated with scores on the CTS-R (r = .54, p < .01). Moreover, the Collaboration subscale of the CCC-RS was significantly correlated (r = .44) with its counterpart of the CTS-R in a theoretically predictable manner. Conclusions: These preliminary results indicate that the CCC-RS is a reliable measure with adequate face, content and convergent validity. Further research is needed to replicate and extend the current findings to other facets of validity.