A 3 1/2-year-old boy presented on three occasions with painful, itchy, oedematous plaques on his limbs. On two occasions he had received hepatitis B vaccination 11-13 days previously, and on the third occasion received triple antigen (DTP) vaccination 10 days earlier. Skin biopsy revealed a prominent infiltrate of eosinophils involving the entire thickness of the dermis. In addition there were prominent 'flame figures' consisting of eosinophilic necrotic collagen surrounded by granular basophilic debris. The clinical and histological pictures were consistent with Wells' syndrome. The eruption settled on the second and third occasions with 0.1% mometasone furoate cream. Subsequent patch testing showed 2+ reaction to preservative thiomersal at 96 hours. This is the first description of Wells' syndrome with typical clinical and histopathological features associated with thiomersal in two different vaccines.