The early infantile onset ''congenital'' variant of Rett syndrome presents with deviations of behavior from very early infancy. Here, we report on a clinical-genetic study in a collected series of 14 Swedish girls with early infantile onset Rett syndrome phenotype. The clinical diagnosis was based on symptom onset before the age of 6 months and the patients fulfilled 3 or more Rett variant criteria and 5 or more supportive criteria. Genotype-phenotype correlation studies in the CDKL5-gene have recently shown clinical associations to early infantile onset Rett variants. Mutation analyses for both the MECP2-gene and the CDKL5-gene were, therefore, performed. Of interest, we found a large deletion covering 2 exons in MECP2, which underlines the importance of MECP2 mutation screening even for the ''atypical'' early infantile onset variants of Rett syndrome. No early infantile onset Rett syndrome patients in this study had the previously well-known hotspot mutations in the MECP2-gene.