Primary cutaneous actinomycosis is very uncommon because of the exclusively endogenous habitat of the organism. We report a case of primary cutaneous actinomycosis characterized by histopathological "sulfur granules". The patient had a well-defined subcutaneous nodule on the left thigh without any other lesion and was treated with surgical excision and subsequent oral ampicillin for six weeks. There has been no recurrence during a 1-year period of follow-up.