This longitudinal study aimed to evaluate qualitative (parosmia) and quantitative (hyposmia/anosmia) olfaction 2–4 weeks (baseline) and 6 months (follow-up) after a mild traumatic brain injury (mTBI). We further evaluated the predictive value of baseline depression, anxiety, and olfaction scores on depression and anxiety at follow-up. At baseline, olfactory function and affective state were assessed in 107 participants (53 patients with mTBI; 54 healthy controls). At follow-up, data were collected on 71 participants (32 patients and 39 controls). Both at baseline and follow-up, patients with mTBI showed more signs of parosmia, depression, and anxiety compared with controls. However, patients did not, neither at baseline nor follow-up, show quantitative olfactory impairment. Moreover, although baseline scores of depression and anxiety helped predict the development of symptoms of depression and anxiety at follow-up, adding parosmia scores to the prediction model significantly increased the amount of explained variances. Clinicians should implement affective and olfactory evaluation to predict patients’ affective outcome.

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