Ethnic disproportionality among students with mental retardation and relationships between disproportionality and sociodemographic factors were investigated. Using national data, we examined the effects of gender, ethnicity, and sociodemographic factors on the proportion of students identified as having mental retardation. Results indicate a clear association among ethnicity, gender, and mental retardation. Sociodemographic variables were also strongly associated with the proportion of students identified. A logistic regression model that included sociodemographic predictors was significantly better than models with gender and race alone. Findings indicate that both individual student characteristics and district sociodemographic characteristics were important in determining the likelihood of identification of mental retardation and that the impact of the sociodemographic characteristics is different for each gender/ethnicity group. Recommendations for future research are provided.