Glial fibrillary acidic protein (GFAP) and ubiquitin C-terminal hydrolase-L1 (UCH-L1) have been studied as potential biomarkers of mild traumatic brain injury (mTBI). We report the levels of GFAP and UCH-L1 in patients with acute orthopedic injuries without central nervous system involvement and relate them to the type of extracranial injury, head magnetic resonance imaging (MRI) findings, and to the levels of GFAP and UCH-L1 in patients with computed tomography (CT) negative mTBI. Serum UCH-L1 and GFAP were longitudinally measured from 73 patients with acute orthopedic injury on arrival and on days 1, 2, 3, 7 after the admission, and on the follow-up visit 3-10 months after the injury. The injury types were recorded and 71% patients underwent also head MRI. The results were compared to those found in patients with CT-negative mTBI (n=93). The levels of GFAP were higher in patients with acute orthopedic trauma than in patients with CT-negative mTBI (p=0.026) on arrival, but no differences were found on the following days. The levels of UCH-L1 were not significantly different between these two groups at any measured point of time. Levels of GFAP and UCH-L1 were not able to distinguish patients with CT-negative mTBI from patients with orthopedic trauma. Patients with orthopedic trauma and high levels of UCH-L1 or GFAP values may be falsely diagnosed as having a concomitant mTBI, predisposing them to unwarranted diagnostics and unnecessary brain imaging. This casts a significant doubt on their diagnostic value in cases with mTBI.