On the first day of life, a healthy infant was given a recombinant hepatiti
s B vaccine. Over the following year, a 3 by 4.5 cm, well-defined, erythema
tous patch with an overlying white, reticulated, smaller plaque gradually a
ppeared on her thigh at the vaccination site. Darier's sign was elicited at
the site. Examination of a biopsy specimen showed an upper dermal mast cel
l infiltrate, This is the first reported case of a solitary mastocytoma app
earing in a vaccination site.