Immunosuppressive drugs are commonly used for the treatment of inflammatory bowel disease. Patients receiving immunosuppressants are susceptible to a variety of infections with opportunistic pathogens. We present a case of skin infection with Mycobacterium chelonae in a 60-year-old Caucasian woman with ulcerative colitis who had been treated with corticosteroids and azathioprine. The disease manifested with fever and rash involving the right leg. Infliximab was administered due to a presumptive diagnosis of pyoderma gangrenosum, leading to worsening of the clinical syndrome and admission to our hospital. Routine cultures from various sites were all negative. However, Ziehl-Neelsen staining of pus from the lesions revealed acid-fast bacilli, and culture yielded a rapidly growing mycobacterium further identified as M. chelonae. The patient responded to a clarithromycin-based regimen. Clinicians should be aware of skin lesions caused by atypical mycobacteria in immunocompromised patients with inflammatory bowel disease. Furthermore, they should be able to thoroughly investigate and promptly treat these conditions.