Porokeratosis is a genodermatosis characterized by abnormal epidermal keratinization with the histologic finding of cornoid lamella. Porokeratosis of Mibelli may be autosomal dominant or sporadic. Currently, there is no established cure for this disease and few clinical trials have been published worldwide. We describe a case of a 56-year-old man with a seventeen year history of a solitary erythematous plaque with raised border along the left midaxillary line, originating from a papule which was burned by a cigarette. Review of skin punch biopsy which was initially read as keloid with signs of irritation showed columns of parakeratosis with underlying necrotic keratinocytes, consistent with porokeratosis. Topical 4% 5-fluorouracil in propylene glycol was applied twice daily which resulted in an inflammatory response after 3 weeks of use. This gradually resolved with notable decreased thickness of the plaque.