Background: We recently reported frequent use of opioids among elderly with dementia. Discrepancies in clinical practice may in part explain the higher use of opioids in elderly with dementia, which geographical variation may be able to clarify. Objective: To investigate geographical variation in opioid use in elderly with dementia compared to elderly without dementia. Methods: Register-based cross-sectional study in the entire elderly (≥65 years) population of Denmark in 2015. Data included place of residence, prescriptions, and discharge diagnoses from hospital contacts. Prevalence of opioid use among elderly with (n = 36,014) and without dementia (n = 1,011,787) was compared nationwide across the five Danish regions using logistic regression analysis and for the 98 municipalities using age and sex standardization. Results: 32.5% of elderly with dementia and 16.9% without were treated with an opioid in 2015. For home-living elderly with dementia, there was a 4-fold difference in opioid use (9.4 to 36.8%) between municipalities compared to a 1.6-fold (12.7 to 20.2%) difference for elderly without. In nursing home residents there was a 2-fold difference (dementia: 26.5 to 55.2%; no dementia: 31.8 to 60.4%). Differences between the five regions were minor. Conclusion: Opioid use in elderly with dementia was frequent and almost twice as high compared to elderly without dementia, which may challenge patient safety. The pronounced geographical variations at municipality level, particularly among elderly with dementia, indicate differences in the approach to treatment of chronic pain in primary care. Our study suggests that more guidance on treatment of pain in elderly with dementia is needed.