L2 motivation research has a longstanding monolingual bias. Recently, however, the motivational systems of a multilingual's different languages have been conceptualised as constituting a multilingual motivational system, and it has been suggested that interactions between the ideal Lx self and the ideal Ly self can lead to the emergence of an ideal "multilingual" self. While the notion of an ideal multilingual self chimes with research on multilinguals' identity experiences, it has not been investigated empirically. The purpose of this study is to establish whether there is empirical support for the proposed ideal multilingual self construct, and whether it influences motivation to learn a second foreign language. A questionnaire containing items measuring the ideal L2 self and the ideal multilingual self was administered to a sample of secondary students (N = 323) at two schools in Sweden with international profiles. Using structural equation modelling, analyses yielded discriminant validity for the ideal multilingual self construct, and revealed an indirect influence on intended effort mediated via the ideal L2 self. On the strength of these results, a case is made for future research into people's motivation to be or become multilingual, and educational interventions focused on developing students' ideal multilingual selves.