BACKGROUND: Infections are one of the major causes of death in patients with advanced-stage mycosis fungoides (MF) or Sezary syndrome (SS). However, few recent data are available on the characteristics and risk factors of these infectious events. OBJECTIVES: To describe infectious events occurring in a cohort of patients with MF/SS, and to identify associated clinical and biological risk factors. METHODS: A retrospective cohort study was performed to investigate infectious events and associated factors in patients diagnosed with MF (stage IB and beyond) or SS followed from May 2011 to May 2016 at the University Hospital of Bordeaux, France. RESULTS: Seventy-one patients with complete follow-up were included. Eighty infectious events were recorded in 40 patients, including 28 skin and soft tissue infections and 25 cases of pneumonia. Opportunistic infections, which are usually associated with depleted cell-mediated immunity, were scarce (9%). In multivariate analysis, cardiac, renal or lung comorbidities [odds ratio (OR) 7.2, 95% confidence interval (CI) 3.3-15.9; P = 0.002], SS (OR 8.8, 95% CI 7.7-10.2; P = 0.037) and lymphocyte count < 0.5 x 10(9) cells L(-1) (OR 6.4, 95% CI 1.5-27.4; P = 0.004) were significantly associated with a higher risk of infection. CONCLUSIONS: Opportunistic germs were rarely recorded, but their incidence was probably prevented by adequate prophylaxis (ongoing in 28% of patients). As in patients living with AIDS, pneumonias were frequent. On the other hand, bacterial cutaneous infections represent a specific pattern in patients with MF/SS. Patients with chronic organ failure, lymphocytopenia and SS should be considered as being at high risk for infectious events. Pneumococcal vaccination should be systematically recommended, and prophylaxis with co-trimoxazole and valaciclovir when the CD4 count is < 0.2 x 10(9) cells L(-1) .Read less <