PURPOSE: There is little evidence regarding the effects of dental status on body mass index (BMI) in inpatients with schizophrenia. Thus, we performed a cross-sectional study to explore the associations between the number of remaining teeth and BMI in Japanese inpatients with schizophrenia. PATIENTS AND METHODS: We performed multiple regression analysis to assess the effects of potential predictors (age, sex, number of remaining teeth, number of antipsychotics prescribed, chlorpromazine equivalent dose, and antipsychotic type) on BMI in 212 inpatients with schizophrenia. We then compared the number of remaining teeth between inpatients with schizophrenia and the Japanese general population (3283 individuals) from the Japan Dental Diseases Survey 2016, using an analysis of covariance with age and sex as covariates. RESULTS: Multiple regression analysis showed that the number of remaining teeth and the number of antipsychotics prescribed were significantly correlated with BMI (standardized regression coefficient = 0.201 and 0.235, respectively). In the analysis of covariance, inpatients with schizophrenia had significantly fewer remaining teeth compared with the Japanese general population (mean 14.8 [standard deviation: 10.9] vs mean 23.0 [standard deviation: 8.1]). CONCLUSION: These results suggested that tooth loss and antipsychotic polypharmacy affect BMI in inpatients with schizophrenia, and that inpatients with schizophrenia lose more teeth compared with the general population.