This study evaluated a relaxation intervention designed to prevent anxiety during magnetic resonance imaging (MRI), and assessed the development of fears in patients who felt anxious during the procedure. Patients were assigned to a control condition (no intervention; n = 52), relaxation before the scan (n = 44), or relaxation before and during the scan (n = 43). Compared to the control group, patients who practised relaxation showed reduced anxiety during the scan. Seven months or more after undergoing MRI, there was a positive correlation between anxiety experienced during the scan and the development of MRI-related fears. The intervention did not prevent the development of MRI-related fears at follow-up.