Sweet's syndrome or acute febrile neutrophilic dermatosis is characterised by the abrupt onset of painful erythematous plaques or nodules, pyrexia (>38°F) and histopathologic evidence of a dense neutrophilic infiltrate without vasculitis. It has been reported in association with many diseases, however, its association with Hashimoto's thyroiditis is rare. A 47-year-old Filipino woman with a 30-year history of an asymptomatic anterior neck mass developed painful, erythematous annular plaques on her arms with associated fever. Skin biopsy confirmed the diagnosis of Sweet's syndrome. The anterior neck mass was confirmed to be Hashimoto's thyroiditis. This is a rare association with only two reported cases in the literature. There are no published cases in the Philippines on Sweet's syndrome and Hashimoto's thyroiditis to date.