The analysis of the process of collaboration is a central topic in current CSCL research. However, defining process characteristics relevant for collaboration quality and developing instruments capable of assessing these characteristics are no trivial tasks. In the assessment method presented in this paper, nine qualitatively defined dimensions of collaboration are rated quantitatively: sustaining mutual understanding, dialogue management, information pooling, reaching consensus, task division, time management, technical coordination, reciprocal interaction, and individual task orientation. The data basis for the development of these dimensions was taken from a study in which students of psychology and medicine collaborated on a complex patient case via a desktop-videoconferencing system. A qualitative content analysis was performed on a sample of transcribed collaboration dialogue. The insights from this analysis were then integrated with theoretical considerations about the roles of communication, joint information processing, coordination, interpersonal relationship, and motivation in the collaboration process. The resulting rating scheme was applied to process data from a new sample of 40 collaborating dyads. Based on positive findings on inter-rater reliability, consistency, and validity from this evaluation, we argue that the new method can be recommended for use in different areas of CSCL.