The artificial language Esperanto is spoken not only as a second language, by its proponents, but also as a native language by children of some of those proponents. The present study is a preliminary description of some characteristics of the Native Esperanto (NE) of eight speakers, ranging in age from six to fourteen years. As such, it is the first of its kind – previous works on NE are either theoretical treatises or individual case studies. We find, at least for the eight subjects studied, both bilingualism and nativization effects, differentiating native from non-native Esperanto speech. Among these effects are loss or modification of the accusative case, phonological reduction, attrition of the tense/aspect system, and pronominal cliticization. The theoretical ramifications are discussed, particularly with regard to universals of language acquisition and the effects of expressive requirements of language.