Experimental research suggests the differentiation of ‘nice’ and ‘nasty’ theory of mind (ToM). Over 5000 parents from the Twins Early Development Study reported on nice (e.g., being considerate) and nasty (e.g., blaming others) behaviours following their twins’ second, third, and fourth birthdays. Factor analyses yielded four factors and it was proposed that these related to prosocial behaviour necessitating ToM (Nice ToM), antisocial behaviour necessitating ToM (Nasty ToM), and prosocial and antisocial behaviour not necessitating ToM (Nice and Nasty). Interscale correlations, gender differences, and their relationship with language were consistent with this distinction. Both ToM scales showed moderate heritability and significant environmental influences (shared and nonshared). Bivariate analyses indicated somewhat distinct aetiological influences on Nice ToM versus Nasty ToM. However, further research is needed to confirm whether this distinction reflects interactions between ToM and temperament, or two underlying genetic and cognitively distinct ToM abilities.