The aim is to describe an ultrasound procedure that evaluates the prevertebral soft tissue (PST) and upper airway and investigate the compatibility between X-ray and ultrasonography in PST evaluation. We included 11 radiculopathy/myelopathy patients who underwent anterior cervical decompression and fusion involving C5/6, C6/7, or both segments. The condition of the PST and upper airway was evaluated over 14 days. The Bland–Altman method was used to evaluate the degree of agreement between the PST values obtained using radiography versus ultrasonography. The Pearson correlation coefficient was used to determine the relationship between the PST measurement methods. Single-level anterior cervical decompression and fusion (ACDF) was performed in 8 cases and double-level ACDF, in 3 cases. PST and upper airway thickness peaked on postoperative day 3, with no airway complications. The Bland–Altman bias was within the prespecified clinically nonsignificant range—0.13 ± 0.36 mm (95%CI 0.04–0.22 mm). Ultrasonography effectively captured post-ACDF changes in PST and upper airway thickness and detected airway edema. Ultrasonography can help continuously assess the PST and upper airway as it is simple and has no radiation exposure risk. Therefore, radiography alone is insufficient for post-ACDF detection of airway complications and including ultrasonography may be beneficial.