Introduction: Coping skills training interventions have been found to be efficacious in helping both patients and their partners manage the physical and emotional challenges they face following a cancer diagnosis. However, many of these interventions are costly and not sustainable. To overcome these issues, a self-directed format is increasingly used. The efficacy of self-directed interventions for patients has been supported; however, no study has reported on the outcomes for their partners. This study will test the efficacy of Coping-Together - a multimedia, self-directed, coping skills training intervention for patients with cancer and their partners. Methods and analysis: The proposed three-group, parallel, randomised controlled trial will recruit patients diagnosed in the past 4 months with breast, prostate, colorectal cancer or melanoma through their treating clinician. Patients and their partners will be randomised to (1) a minimal ethical care (MEC) condition - selected Cancer Council New South Wales booklets and a brochure for the Cancer Council Helpline, (2) Coping-Together generic - MEC materials, the six Coping-Together booklets and DVD, the Cancer Council Queensland relaxation audio CD and login to the Coping-Together website or (3) Coping-Together tailored - MEC materials, the Coping-Together DVD, the login to the website and only those Coping-Together booklet sections that pertain to their direct concerns. Anxiety (primary outcome), distress, depression, dyadic adjustment, quality of life, illness or caregiving appraisal, self-efficacy and dyadic and individual coping will be assessed before receiving the study material (ie, baseline) and again at 3, 6 and 12 months postbaseline. Intention-to-treat and per protocol analysis will be conducted. Ethics and dissemination: This study has been approved by the relevant local area health and University ethics committees. Study findings will be disseminated not only through peer-reviewed publications and conference presentations but also through educational outreach visits, publication of lay research summaries in consumer newsletters and publications targeting clinicians.