Mycobacterium marinum infection is rare, misrecognized and underdiagnosed but can cause severe clinical pictures, especially if the diagnosis is late and the patient is immunocompromised. Treatment includes long-term antibiotic therapy combined with surgical therapy when necessary. We performed a multicenter retrospective study with data from five Italian hospitals describing the epidemiological, clinical, bacteriological characteristics, and treatment outcome of subjects diagnosed with M. marinum infection. During the study period 17 subjects were enrolled. The median time from symptoms onset to diagnosis was 124 days. Thirteen out of 17 were bacteriologically confirmed cases. In all cases, expect one, at least two antibiotics were used with a median of 6 months of treatment, leading to clinical resolution. Too often, the diagnosis of M. marinum infection is delayed and it remains largely presumptive. Prospective studies and randomized controlled trials are necessary to better understand the most appropriate therapeutic regimen and duration.