Cutaneous T-cell lymphomas (CTCL), especially mycosis fungoides, can be considered as a state of longstanding low-grade systemic inflammation. Many studies have focused on secondary cancers with CTCL, but information about comorbidities is limited. A total of 144 patients with CTCL at Helsinki University Central Hospital during 2005 to 2015 were studied to determine associated comorbidities and causes of death in this cohort. Compared with an age-standardized control population, the prevalence of type 2 diabetes mellitus was increased among patients with CTCL with no link to obesity. Patients with CTCL had a lower prevalence of hypertension, myocardial infarction and stroke than the control group. The 3 most common causes of death were CTCL, coronary artery disease and lung cancer. The increased risk of myocardial infarction or stroke reported previously was not detected in this patient group.