Search of the literature reveals only one instance of the occurrence of pilonidal cysts and sinuses in identical twins.1 The following report of such an occurrence is interesting also because of the appearance of the symptoms at approximately the same time in the two twins:
I. K. and J. K., identical twins, aged 23, in December 1935, within a period of a few days, each noticed a symptom free lump at the end of the spine. One year later, again within a few days, both lumps began to drain very slightly. The drainage was serous and in one patient remained so. The other patient had a mild inflammatory reaction in March 1937 with some soreness for several days.
Examination revealed in each case two small openings in the midline over the coccyx into which probes could be inserted about 2 cm. and from which there escaped a small amount