Traumatic brain injury (TBI) is associated with atherosclerosis and cardiovascular mortality. However, the causal relationship between TBI and atherosclerosis is unclear. This study aimed to evaluate insulin resistance in patients with TBI and its relationship with clinical and demographic characteristics of the patients. The case-controlled study included 60 patients with moderate and severe TBI in the chronic phase and 60 healthy controls matched for sex, age, and body mass index (BMI). Demographic characteristics, serum insulin, and fasting blood glucose levels of both groups were assessed. Insulin resistance was determined by the Homeostasis Model Assessment insulin resistance. The clinical features of the TBI group were also recorded. Insulin resistance was observed to be higher in the TBI group than in the control group (46.7% vs. 18.33%, P = 0.002). However, no significant difference was determined between TBI patients with and without insulin resistance in terms of all demographic and clinical parameters examined (all P > 0.05). Age, sex, BMI, and trauma severity were not significant predictors of insulin resistance in TBI patients. Moderate-to-severe TBI patients have more prevalent insulin resistance than healthy controls. Evaluation of insulin resistance in these patients, who currently have limited participation in life activities and healthy lifestyles, may be useful to prevent cardiovascular diseases caused by insulin resistance.