Research on nonverbal synchrony (movement coordination) in psychotherapy has recently attracted increased attention. Nonverbal synchrony has been shown to relate to the therapeutic alliance and outcome. However, research on nonverbal synchrony in couple therapy remains scarce. In this study, we examined the therapy process of one couple in detail and created a coding scheme to depict posture and movement synchrony. In this case study, we found that the relationship between nonverbal synchrony and the therapeutic alliance was complex. During the therapy process, the amount of nonverbal synchrony varied, as did the participants’ evaluations of the alliance. In couple therapy nonverbal synchrony could affect both the persons involved in it and the persons observing it. In one of the sessions, almost all the synchronies occurred between the female client and one of the therapists, and all except the female client evaluated the alliance to be weaker. In this case study, there were two therapists present, and the co-therapists’ synchrony was found to be important for the male client’s evaluations of the alliance. When there was more synchrony between the therapists, he evaluated the alliance to be stronger. Interestingly, the co-therapists’ synchrony seemed to peak in sessions that succeeded sessions with a weaker alliance, as if the therapists were implicitly making a joint effort to strengthen the alliance. A short episode from one session is given to illustrate the findings. Our coding scheme enables studying nonverbal synchrony (posture and movement synchrony) in couple therapy and combining the research results to other temporally precise data obtained from the sessions. More research is needed to validate the method.