Aim Cutaneous manifestations of Sweet's syndrome (SS) are typically painful plaque-forming erythematous papules, while bullae are quite uncommon. We present a case of bullous variant of SS in acute myeloid leukaemia. In this case, herpes infection of the left mandible had preceded the development of SS. Case Report A 75-year-old male with myelodysplastic syndrome first presented with herpes zoster virus infection-like bullae and erosive plaques on the left side of the face and neck. Treatment with valacyclovir and antibiotics was effective only for the initial lesions, whereas the other bullae kept developing predominantly on the left side. Histopathological study revealed epidermal bulla formation, pandermal neutrophilic infiltration, erythrocyte extravasation and subepidermal oedema, but no vasculitis. The findings suggested the diagnosis of bullous variant of SS. Discussion Our case was unique in that bullous SS symptoms developed predominantly on one side of the cheek and neck where the herpes zoster infection occurred prior to SS. The tendency may explain the possible association between viral infection and development of SS.