BACKGROUND: Due to worldwide migration to Western countries, physicians are increasingly encountering patients with different ethnic backgrounds. Communication problems can arise as a result of differences in cultural backgrounds and poor language proficiency. AIMS: To assess the effectiveness of an educational intervention on intercultural communication aimed to decrease inequalities in care provided between Western and non-Western patients. DESIGN OF STUDY: A randomised controlled trial with randomisation at the GP level and outcome measurements at the patient level. SETTING: General practice in Rotterdam. METHOD: Thirty-eight Dutch GPs in the Rotterdam region, with at least 25% of inhabitants of non-Western origin, and 2407 visiting patients were invited to participate in the study. A total of 986 consultations were finally included. The GPs were educated about cultural differences and trained in intercultural communication. Patients received a videotaped instruction focusing on how to communicate with their GP in a direct way. The primary outcome measure was mutual understanding and the secondary outcomes were patient's satisfaction and perceived quality of care. The intervention effect was assessed for all patients together, for the 'Western' and 'non-Western' patients, and for patients with different cultural backgrounds separately. RESULTS: An intervention effect was seen 6 months after the intervention, as improvement in mutual understanding (and some improvement in perceived quality of care) in consultations with 'non-Western' patients. CONCLUSIONS: A double intervention on intercultural communication given to both physician and patient decreases the gap in quality of care between 'Western' and 'non-Western' patients.