Aim — to estimate the prevalence of molar incisor hypomineralisation (MIH) across genders and place of residence as well as its association with dental caries among 12-years-old children in Northwest Russia. Methods. A cross-sectional study included 1233 (653 girls) randomly selected 12-years-old children from 7 urban and 5 rural areas of Arkhangelsk region. MIH and its severity were diagnosed using Weerheijm et al (2003) and Mathu-Muju & Wright (2006) criteria. Dental caries was studied at the D3 level following WHO (2013) recommendations. Prevalence of MIH and caries and means for Decayed-Missing-Filled (DMFT) scores are presented with 95% confidence intervals (CI). Pearson’s chi-squared tests and Mann—Whitney tests were used for dichotomous and numerical data, respectively. The study was approved by the Ethical Committee of the Northern State Medical University, Arkhangelsk, Russia. Results. The overall prevalence of MIH was 2.1% (95% CI: 1.44—3.07). The prevalence of mild MIH was 46.2% (95% CI: 28.8—64.5). Average and severe MIH were diagnosed in 26.9% (95% CI: 13.7—46.1) of children each. The prevalence of caries among those with and without MIH was 100% (95% CI: 87.1—100.0) and 74.8% (95% CI: 72.3—77.2), respectively (p=0.003). DMFT values for children with and without MIH were 4.46 (95% CI: 3.20—5.72) and 2.41 (95% CI: 2.28—2.53), respectively (p<0.001). Conclusions. Although the prevalence of MIH in Northwest Russia is lower than in most other countries our findings suggest that hypomineralised molars are much more prone to caries.