In this report we present the clinical features and molecular and cytogenetic findings in a female with partial trisomy 14q. Molecular and cytogenetic studies allowed us to determine that the extra 14q material (of paternal origin) was translocated postzygotically onto the maternal X chromosome. Consequently, only the derivative X chromosome was inactivated, although inactivation apparently did not spread over the entire chromosome 14q. This partial inactivation makes the present case unusual, giving rise to phenotypic features absent in other patients with partial trisomy 14q, typically restricted to the distal part of the chromosome.