This is the third update of a review that was originally published in the Cochrane Library in 2002, Issue 2. People with cancer, their families and carers have a high prevalence of psychological stress, which may be minimised by effective communication and support from their attending healthcare professionals (HCPs). Research suggests communication skills do not reliably improve with experience, therefore, considerable effort is dedicated to courses that may improve communication skills for HCPs involved in cancer care. A variety of communication skills training (CST) courses are in practice. We conducted this review to determine whether CST works and which types of CST, if any, are the most effective. To assess whether communication skills training is effective in changing behaviour of HCPs working in cancer care and in improving HCP well-being, patient health status and satisfaction. For this update, we searched the following electronic databases: Cochrane Central Register of Controlled Trials (CENTRAL; 2018, Issue 4), MEDLINE via Ovid, Embase via Ovid, PsycInfo and CINAHL up to May 2018. In addition, we searched the US National Library of Medicine Clinical Trial Registry and handsearched the reference lists of relevant articles and conference proceedings for additional studies. The original review was a narrative review that included randomised controlled trials (RCTs) and controlled before-and-after studies. In updated versions, we limited our criteria to RCTs evaluating CST compared with no CST or other CST in HCPs working in cancer care. Primary outcomes were changes in HCP communication skills measured in interactions with real or simulated people with cancer or both, using objective scales. We excluded studies whose focus was communication skills in encounters related to informed consent for research. Two review authors independently assessed trials and extracted data to a pre-designed data collection form. We pooled data using the random-effects method. For continuous data, we used standardised mean differences (SMDs). We included 17 RCTs conducted mainly in outpatient settings. Eleven trials compared CST with no CST intervention; three trials compared the effect of a follow-up CST intervention after initial CST training; two trials compared the effect of CST and patient coaching; and one trial compared two types of CST. The types of CST courses evaluated in these trials were diverse. Study participants included oncologists, residents, other doctors, nurses and a mixed team of HCPs. Overall, 1240 HCPs participated (612 doctors including 151 residents, 532 nurses, and 96 mixed HCPs).Ten trials contributed data to the meta-analyses. HCPs in the intervention groups were more likely to use open questions in the post-intervention interviews than the control group (SMD 0.25, 95% CI 0.02 to 0.48; P = 0.03, I² = 62%; 5 studies, 796 participant interviews; very low-certainty evidence); more likely to show empathy towards their patients (SMD 0.18, 95% CI 0.05 to 0.32; P = 0.008, I² = 0%; 6 studies, 844 participant interviews; moderate-certainty evidence), and less likely to give facts only (SMD -0.26, 95% CI -0.51 to -0.01; P = 0.05, I² = 68%; 5 studies, 780 participant interviews; low-certainty evidence). Evidence suggesting no difference between CST and no CST on eliciting patient concerns and providing appropriate information was of a moderate-certainty. There was no evidence of differences in the other HCP communication skills, including clarifying and/or summarising information, and negotiation. Doctors and nurses did not perform differently for any HCP outcomes.There were no differences between the groups with regard to HCP 'burnout' (low-certainty evidence) nor with regard to patient satisfaction or patient perception of the HCPs communication skills (very low-certainty evidence). Out of the 17 included RCTs 15 were considered to be at a low risk of overall bias. Various CST courses appear to be effective in improving HCP communication skills related to supportive skills and to help HCPs to be less likely to give facts only without individualising their responses to the patient's emotions or offering support. We were unable to determine whether the effects of CST are sustained over time, whether consolidation sessions are necessary, and which types of CST programs are most likely to work. We found no evidence to support a beneficial effect of CST on HCP 'burnout', the mental or physical health and satisfaction of people with cancer.