Serratia marcescens is a species of gram negative bacillus, classified as a member of the Enterobacteriaceae, mainly involved in opportunistic infections, particulary in the hospital environment. Cutaneous infections have rarely reported in literature and are predominantly observed in elderly or in immunocompromised patients. The clinical manifestations of skin infections include granulomatous lesions, necrotizing fasciitis, nodules, cellulitis, ulcers, dermal abscesses. Infections caused by S. marcescens may be difficult to treat because of resistance to a variety of antibiotics, including ampicillin and first and second generation cephalosporins. Aminoglycosides have good activity against S. marcescens, but resistant strains have also been described. We report a very intriguing case of S. marcescens infection, in an immunocompetent 18-year-old man, causing multiple rounded ulcers of varying sizes, along with few pustular lesions that both clinically and histopathologically mimic a pyoderma gangrenosum (PG). This is a non infectious neutrophilic skin disorder, characterized by painful and rapidly progressing skin ulceration. According to our experience, we would strongly recommend to perform cultures of multiple skin ulcers resembling PG, even in young healthy patients, to ensure correct diagnosis and treatment, since resistant to conventional antibiotics bacteria such as S. marcescens may be the cause of these lesions, like in the case here reported.