Background: While research demonstrates that somatisation is highly correlated with post-traumatic stress disorder (PTSD), the relationship between International Classification of Diseases 11th edition (ICD-11) PTSD, complex PTSD (CPTSD) and somatisation has not previously been determined. Objective: To determine the relationship between frequency and severity of somatisation and ICD-11 PTSD/ CPTSD. Method: This cross-sectional study included 222 individuals recruited to the National Centre for Mental Health (NCMH) PTSD cohort. We assessed rates of Patient Health Questionnaire 15 (PHQ-15) somatisation stratified by ICD-11 PTSD/CPTSD status. Path analysis was used to explore the relationship between PTSD/CPTSD and somatisation, including number of traumatic events, age, and gender as controls. Results: 70% (58/83) of individuals with CPTSD had high PHQ-15 somatisation symptom severity compared with 48% (12/25) of those with PTSD (chi-square: 95.1, p value <0.001). Path analysis demonstrated that core PTSD symptoms and not disturbances in self organisation (DSO) symptoms were associated with somatisation (unstandardised coefficients: 0.616 (p-value 0.017) and − 0.012 (p-value 0.962) respectively. Conclusions: Individuals with CPTSD have higher somatisation than those with PTSD. The core features of PTSD, not the DSO, characteristic of CPTSD, were associated with somatisation