In immunosuppressed patients, a high rate of complications due to opportunistic infection is known. We report the case of a 36 year old patient with ulcerative colitis and a septic complication with ongoing pancytopenia. Due to colonic perforation, colectomy had to be performed. Despite this intervention, the septic constellation persisted. The pancytopenia in peripheral blood counts also persisted with the necessity of repetitive transfusions. A bone marrow biopsy showed an infiltration with Leishmania bodies in macrophages. Tissue culture allowed for typing of the parasites as belonging to the L. donovani/infantum complex, DNA sequencing confirmed infection with L. infantum. This infection must have been contracted during a vacation on Mallorca about 1.5 years earlier. Administration of liposomal amphotericin B cured the patient. Surprisingly, histological examination of the resected colon reveiled the presence of an immunoblastic B-cell lymphoma. In this case, immunosuppression was a prerequisite for the manifestation of leishmaniosis.