Purpose: To evaluate caries experience in primary molars as well as the differences in caries prevalence and caries lesion location on individual tooth surfaces between first and second primary molars in pre-school children. Materials and Methods: A cross-sectional study was conducted on 307 children, aged 3 to 5 years, from randomly chosen kindergartens in Lodz, Poland. Caries experience was scored according to WHO recommendations. The caries intensity (dmft, dmfts) for first and second primary molars was calculated. In addition, the percentage of particular surfaces with caries was counted for each molar separately. Results: The mean dmft for primary molars was 1.84 (dmfts = 2.47) and dmft > 0 was seen in 53.09% of the study subjects. While in the entire examined population dmft and dmfts for first and second molars did not differ significantly, in 5-year-old children, the left mandibular first molar was associated with a higher caries intensity than the left mandibular second molar (dmfts = 0.465 vs 0.344, Z = -1.98, p = 0.04). However, in 5-year-olds, higher caries occurrence was seen for occlusal surfaces of the tooth 85 than 84 (33.62% vs 20.68%, χ2 = 4.09, p = 0.03). The distal surface was more frequently affected in first molars than in second molars in children aged 4 (85 vs 84, χ2 = 17.1, p 0.001; 75 vs 74, χ2 = 11.5, p = 0.007, 55 vs 54; χ2 = 4.6, p = 0.03) and 5 years (54 vs 55, χ2 = 20.09; 64 vs 65, χ2 = 16.75; 74 vs 75, χ2 = 21.6; 84 vs 85, χ2 = 31.07; all comparisons p 0.001). In contrast, the mesial surfaces of mandibular second molars demonstrated more caries than the homologous surfaces of first molars, both in 4-year-olds (85 vs 84, χ2 = 6.15, p = 0.01) and 5-year-olds (75 vs 74, χ2 = 3.9, p = 0.04). Conclusion: In 5-year-old children, caries of occlusal and mesial surfaces was more common in primary second molars. However, distal surfaces were affected more in first than second molars. Keywords: deciduous molars, dental caries, pre-school children, tooth surface