Traumatic brain injury can cause endocrine dysfunction, particularly in the pituitary and thyroid. Onychomycosis is a frequent fungal disorder of nails and toes in normal adults and can be associated with hypothyroidism. We present a 35 years old, Chinese male who was affected by Onychomycosis, hypothyroidism, and severe traumatic brain injury (TBI). Onychomycosis was present before TBI in one finger only but deteriorated during the acute stage of TBI, and improved significantly only after the introduction of thyroid treatment.