Background: Dental caries is among the most prevalent chronic diseases in children worldwide, assessed using the decayed-extracted filled teeth index for primary teeth and the Decayed-Missing-Filled Teeth index for permanent teeth. Nutritional status, measured by body mass index, may share common behavioral risk factors with dental caries. However, previous studies have reported inconsistent findings. Purpose: This study aimed to analyze the relationship between body mass index and combined caries experience among 10–12-year-old schoolchildren in Surabaya, Indonesia. Methods: This cross-sectional study included 51 schoolchildren aged 10–12 years at Elementary School (sekolah dasar negeri/SDN) Keputran, Surabaya. Body mass index was calculated from measured body weight and height. Dental caries was assessed according to World Health Organization criteria using the decayed-extracted-filled teeth and Decayed-MissingFilled Teeth indices. The combined caries score was correlated with body mass index using Spearman correlation and negative binomial regression at a significance level of p < 0.05. Results: The mean body mass index was 17.70 ± 4.04 kg/m². The mean decayed-extracted-filled teeth, Decayed-Missing-Filled Teeth, and combined scores were 0.78 ± 1.51, 1.35 ± 2.05, and 2.14 ± 2.48, respectively. Spearman correlation showed a significant negative correlation between body mass index and combined caries experience (r = -0.33; p = 0.018). Regression analysis indicated that each one-unit increase in body mass index was associated with a lower combined caries score (incidence rate ratio = 0.87; 95% confidence interval: 0.79–0.96; p = 0.007). Conclusion: Body mass index showed a significant inverse relationship with combined caries experience among 10–12-year-old schoolchildren. Higher body mass index values were associated with lower combined caries scores.