OBJECTIVES: To estimate the potential unmet need for Magnetic Resonance Imaging (MRI) among Medicare patients with pacemaker implants, via the prevalence of diagnoses and conditions for which MRI is the preferred investigation method. METHODS: The data analyzed comprised of fee-for-service portion of the 2008 Medicare patient population. Using this sample, two issues were examined: the prevalence of the diseases for which MRI is the preferred imaging modality, and the uptake rates of all imaging modalities for MRI-indicated beneficiaries with pacemaker implants compared with those having no implants. For each of those diseases for which MRI is the preferred modality we also identified any trade-offs between lower MRI rates and higher rates for other imaging modalities in pacemaker-implanted compared with non-implanted patients. RESULTS: There was almost no use of MRI in the pacemaker-implanted population, whereas 13% of patients without any kind of implant received an MRI in 2008.  Clinical practice appears in line with the contraindication for MRI in pacemaker-implanted patients. Cancer of the CNS and suspected Stroke are conditions which require timely, accurate imaging for good therapeutic decision making.  A total of 73% and 41% of non-paced subjects received whole body MRI for these conditions respectively, compared with 1% of paced subjects for each disease.  Similar diagnostic discrepancies were observed for Motion disorders, Dementia, Chronic orthopaedic pain and spinal disorders.  Pacemaker implanted patients also had high rates of co-morbidities. CONCLUSIONS: There seems to be a large unmet clinical need for pacemakers and other implanted cardiac devices which allow MRI to be used as a diagnostic method.  The very high rate of MRI use in non-implanted patients with acute, progressive and often fatal conditions of stroke and cancer, and its absence of use in the same patient groups with implants is a concern.  The use of MRI conditional cardiac devices would facilitate greater diagnostic method choice.