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STUDY DESIGN This was a retrospective cohort study. OBJECTIVE The present study is the first to investigate whether cervical paraspinal sarcopenia is associated with cervicothoracic sagittal alignment parameters after posterior cervical fusion (PCF). SUMMARY OF BACKGROUND DATA Few studies have investigated the association between sarcopenia and postoperative outcomes after cervical spine surgery. METHODS We retrospectively reviewed patients undergoing PCF from C2-T2 at a single institution between the years 2017-2020. Two independent reviewers utilized axial cuts of T2-weighted magnetic resonance imaging sequences to perform Goutallier classification of the bilateral semispinalis cervicis (SSC) muscles. Cervical sagittal alignment parameters were compared between subgroups based upon severity of SSC sarcopenia. RESULTS We identified 61 patients for inclusion in this study, including 19 patients with mild SSC sarcopenia and 42 patients with moderate or severe SSC sarcopenia. The moderate-severe sarcopenia subgroup demonstrated a significantly larger change in C2-C7 sagittal vertical axis (+6.8 mm) from the 3-month to 1-year postoperative follow-up in comparison to the mild sarcopenia subgroup (-2.0 mm; P=0.02). The subgroup of patients with moderate-severe sarcopenia also demonstrated an increase in T1-T4 kyphosis (10.9-14.2, P=0.007), T1 slope (28.2-32.4, P=0.003), and C2 slope (24.1-27.3, P=0.05) from 3-month to 1-year postoperatively and a significant decrease in C1-occiput distance (6.3-4.1, P=0.002) during this same interval. CONCLUSIONS In a uniform cohort of patients undergoing PCF from C2-T2, SSC sarcopenia was associated with worsening cervicothoracic alignment from 3-month to 1-year postoperatively.