Objective <p>To quantitatively assess changes in the dimensions of infrahyoid and suprahyoid muscles following neck dissection (ND) in head and neck cancer patients.</p> Methods <p>This study retrospectively analyzed 61 head and neck cancer patients who underwent selective or therapeutic neck dissection at a tertiary medical center between June 2010 and April 2022. The study protocol was approved by the institutional Helsinki Committee. Eligible participants had no procedures directly impacting strap muscles (e.g., thyroidectomy, tracheostomy). Preoperative and postoperative PET-CT scans were analyzed to measure dimensions of digastric, mylohyoid, and infrahyoid muscles, with measurements of the rectus capitis posterior major muscle serving as a control. Statistical analysis was conducted using a two-way ANOVA within a linear mixed-effects model framework to assess changes in muscle dimensions pre- and post-operation.</p> Results <p>Postoperative reductions in the dimensions of infrahyoid and suprahyoid muscles on the operated side were significant (<i>p</i> &lt; 0.001), while the rectus capitis posterior major muscle remained unchanged (<i>p</i> &gt; 0.05). No significant changes were observed on the non-operated side. The mylohyoid muscle exhibited greater susceptibility to radiation and modified neck dissection (<i>p</i> = 0.0049, <i>p</i> = 0.0225, respectively). Tumor size and chemotherapy did not significantly influence muscle atrophy.</p> Conclusion <p>The findings indicate that neck dissection leads to significant postoperative atrophy of infrahyoid and suprahyoid muscles, likely due to surgical trauma, denervation, and postoperative fibrosis. This atrophy may have important implications for postoperative recovery and functional outcomes in head and neck cancer patients, highlighting the need for further research on its impact on quality of life.</p> Level of evidence <p>Level III.</p>