BACKGROUND There is an increasing emphasis on the development of communication skills for dietitians but few evidence-based assessment tools available. The present study aimed to develop a dietetic-specific, short, reliable and valid assessment tool for measuring communication skills in patient consultations: DIET-COMMS. METHODS A literature review and feedback from 15 qualified dietitians were used to establish face and content validity during the development of DIET-COMMS. In total, 113 dietetic students and qualified dietitians were video-recorded undertaking mock consultations, assessed using DIET-COMMS by the lead author, and used to establish intra-rater reliability, as well as construct and predictive validity. Twenty recorded consultations were reassessed by nine qualified dietitians to assess inter-rater reliability: eight of these assessors were interviewed to determine user evaluation. RESULTS Significant improvements in DIET-COMMS scores were achieved as students and qualified staff progressed through their training and gained experience, demonstrating construct validity, and also by qualified staff attending a training course, indicating predictive validity (P < 0.05). An acceptable level of intra-rater reliability (rs = 0.90) and a moderate level of inter-rater reliability (r = 0.49) were demonstrated. Interviews identified many positive features and possible uses for DIET-COMMS in both pre- and post-registration settings. The need for assessor training was emphasised and how readily qualified dietitians would accept assessment of skills in practice was questioned. DISCUSSION DIET-COMMS is a short, user-friendly, reliable and valid tool for measuring communication skills in patient consultations with both pre- and post-registration dietitians. Additional work is required to develop a training package for assessors and to identify how DIET-COMMS assessment can acceptably be incorporated into practice.