Although self-reports are often distorted by response biases, nearly all knowledge about interests rely on self-reports. This multiple-rater twin study investigated the degree to which interest self-reports reflect substance. Specifically, we examined whether genetic variance in interest self-reports reflect substance in terms of genetically based motivational attributes or artifact in terms of genetically influenced self-rater biases. We compared normative and ipsatized self- and peer reports on interests from 844 individuals (incl. 225 monozygotic and 113 dizygotic twin pairs) regarding psychometric qualities and further regarding the estimates of genetic and environmental components in self-other agreement and self-rater specificity. Ipsatized interest scores showed lower internal consistency but higher consensus and self-other agreement. Self-other agreement showed a large genetic component, whereas variance specific to self-reports was not significantly attributable to genetic influences. The results provide strong support that genetic variance in interest self-reports reflect substance rather than artifact.