SUMMARY Absence of sweat glands, hypotrichosis, hypodontia, characteristic facial features, and intolerance to heat, without dystrophia of the nails, are manifestations of sex linked hypohydrotic ectodermal dysplasia. Three males and two females were affected in a family in which the affected females were also carrying a pericentric inversion of chromosome 9. Those phenotypically normal females in this pedigree who were obligate carriers had normal karyotypes. One of the affected females (the proband) had, in addition, primary amenorrhoea, absence of thle mammary glands, and rudimentery internal genitalia.The fact that the clinical manifestations of ectodermal dysplasia in the carrier females of this family are only observed in those also carrying a pericentric inversion of chromosome 9 in peripheral blood leucocytes perhaps suggests that non-random inactivation of the paternal X chromosome has occurred as a consequence of the inversion.Anhidrotic ectodermal dysplasia or, more cautiously, hypohydrotic ectodermal dysplasia, is a well known syndrome. Several variant forms have been described, characterised by the presence of associated findings and different modes of inheritance.' The most common X linked form is characterised by severe affection of the males with occasional minor manifestations in heterozygous females. Severe manifestations in females have been reported and explained by the unproved possible presence of a double dose of the gene.2 Pericentric inversion of chromosome 9 (inv 9) has been considered to be a non-harmful polymorphism3 with certain reservations.4 The incidence of this polymorphism varies with races but is generally around 1.5%.3We report an unusual kindred in which several males exhibit typical anhidrotic ectodermal dysplasia, and in which in two sisters this condition occurs in association with a pericentric inversion of chromosome 9. Case reports CASE IThis patient (fig 1) was referred to us at the age of 19 because of the absence of secondary sexual character-*Present address: