Objective: To assess the frequency and factors associated with posttraumatic olfactory dysfunction, including anosmia, in a follow-up of patients with moderate and severe traumatic brain injury (TBI). Methods: The setting was a cross-sectional study of patients that were consecutively included in the Trondheim TBI database, comprising injury-related variables. Eligible participants 18–65 years were contacted 9–104 months post trauma and asked olfactory-related questions. Those reporting possible posttraumatic change of olfaction were invited to further examination using the Sniffin’ Sticks panel. Results: Of 211 eligible participants, 182 (86.3%) took part in telephone interviews and 25(13.7%) were diagnosed with olfactory dysfunction. 60% of these, or 8.2% of all participants, had anosmia. In age-adjusted logistic regression analyses, fall (OR 2.5, 95% CI 1.0–6.2), skull base fracture (OR 2.9, 95% CI 1.2–7.1) and cortical contusion(s) (OR 6.0, 95% CI 2.1–17.3) were associated with olfactory dysfunction. In an analysis of anosmia, fall (OR 3.4, 95% CI 1.1–10.6) and cortical contusion(s) (OR 19.7, 95% CI 2.5-156.0) were associated with the outcome. Conclusion: Of the study participants 13.7% had olfactory dysfunction and 8.2% had anosmia. Higher age, trauma caused by fall and CT displaying skull base fracture and cortical contusion(s) were related to olfactory dysfunction.