Abstract Background Given ongoing demographic and epidemiological transitions, dementia prevalence is expected to rise among both native populations and migrants. Understanding this phenomenon is crucial for healthcare planning. This study, part of the IMMIDEM project (GR-2021-12372081), aims to estimate dementia prevalence in Lazio by migrant status. Methods A cross-sectional study was conducted on individuals aged ≥50, living in Lazio and receiving assistance from the Regional Health Service as of December 31, 2022. A validated algorithm based on Health Information Systems identified patients with dementia. Migrant status was defined by Country of birth, categorized as native Italians, migrants from Highly Developed Countries (HDCs) and from High Migratory Pressure Countries (HMPCs). Age-standardized prevalence of dementia was estimated overall and by migrant status, and 95% confidence intervals (CI) were calculated. Dementia population characteristics were described and compared according to migrant status using χ2test. Results The study included 3,976,160 individuals: 88.9% Italians, 1.7% migrants from HDCs, and 9.4% from HMPCs. Among them, 38,708 had dementia, with a prevalence of 8.48‰ (CI: 8.39-8.57). Dementia prevalence by migrant status was 8.68‰ (CI: 8.58-8.77) in Italians, 6.90‰ (CI: 6.19-7.62) in HDCs migrants, and 5.73‰ (CI:5.37-6.10) in HMPCs migrants. Demographic traits across migrant categories reveal distinct age and gender patterns, with more elderly Italians and a higher male percentage among migrants. From a clinical perspective, Italians showed a higher percentage of circulatory system diseases than migrants (23.5% Italians, 19.2% HDCs, 18.7% HMPCs, p = 0.001), along with a greater percentage of anti-dementia drug prescriptions (54.4% Italians, 50.9% HDCs, 47.4% HMPCs, p < 0.001). Conclusions The study found lower dementia prevalence among migrants compared to native Italians, with reduced access to healthcare services, especially in individuals from HMPCs. Key messages • The dementia prevalence in migrants is lower than in native Italians. • These findings suggest potential underdiagnosis and undertreatment, urging policymakers and healthcare providers to address these healthcare disparities.