BACKGROUND: Since objective stifness measures are not consistent with the patients' perception and its correlation with the clinical severity of neck pain is not clear, novel studies assessing the clinical relevance of muscle stiffness are needed. OBJECTIVES: To analyze the correlation among psychological factors, clinical severity indicators, and muscle stiffness in neck muscles in patients with chronic mechanical neck pain, and compare these factors with asymptomatic controls. METHODS: A cross-sectional observational study was conducted. Participants included cases with chronic neck pain and asymptomatic controls, assessed for muscle stiffness using shear wave elastography, psychological health (anxiety and kinesiophobia), and clinical severity. Data analysis involved correlation matrices and comparison between groups. RESULTS: Although no significant differences in levator scapulae stiffness were observed between groups (p >
0.05), patients exhibited significantly increased stiffness in the anterior scalene and cervical multifidus muscles (p = 0.009 and p = 0.040, respectively). STAI scores were significantly higher in patients for both subscales (STAI-S p = 0.002 and STAI-T p <
0.001), but no kinesiophobic behaviors differences were found (p >
0.05). Significant correlations between pain chronicity, intensity, disability, and psychological factors were confirmed. Notably, the levator scapulae stiffness was positively associated with disability, anxiety, and kinesiophobia (all p <
0.01). However, the anterior scalene and cervical multifidus stiffness, even if significantly associated with demographic factors (p <
0.05), were not associated with clinical or psychological outcomes. CONCLUSION: The findings underscore the intertwined nature of psychological factors and muscle stiffness in chronic neck pain, suggesting the need for integrated approaches in treatment that consider both physical and psychological dimensions.