Twin factor mixture modeling was used to identify temperament profiles while simultaneously estimating a latent factor model for each profile with a sample of 787 twin pairs (M[subscript age] = 7.4 years, SD = 0.84; 49% female; 88.3% Caucasian), using mother- and father-reported temperament. A four-profile, one-factor model fit the data well. Profiles included "regulated, typical reactive," "well-regulated, positive reactive," "regulated, surgent," and "dysregulated, negative reactive." All profiles were heritable, with lower heritability and shared environment also contributing to membership in the "regulated, typical reactive" and "dysregulated, negative reactive" profiles.