Submicroscopic duplications involving <i>SOX3</i> and/or its flanking regions have been identified in 46,XX individuals both with and without disorders of sex development, raising the question whether <i>SOX3</i> overdosage is sufficient to induce testicular development in genetically female individuals. Here, we report a mother-daughter pair with female phenotypes and random X inactivation. The individuals carry complex X chromosomal rearrangements leading to a copy number gain of genomic regions involving <i>SOX3</i> and its upstream region. The amplified DNA fragments were detected at Xq27. These results provide evidence that <i>SOX3 </i>overdosage permits normal sex development in 46,XX individuals with random X inactivation.