Pachyonychia congenita tarda.

Pachyonychia congenita is a rare genetic disorder classified in clinical subtypes. Late onset of the disease has recently been described and designated as pachyonychia congenita tarda. A patient in whom typical manifestations of pachyonychia congenita appeared at the age of 39 years is described. This report substantiates previous observations on the phenomenon of late-onset pachyonychia congenita.