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Background Severe forms of generalised (GD) or cervical dystonia (CD) can be effectively treated with deep brain stimulation (DBS) of the globus pallidus interna (GPi). However, objectively assessing DBS effectiveness remains challenging.Objective To identify objective biomarkers of GPi-DBS effectiveness using a minimalistic three-dimensional (3D) kinematic motion capture system in patients with dystonia.Methods This retrospective longitudinal study analysed kinematic data from 14 patients before and after GPi-DBS: 7 with GD (3 females; mean age, 34.1±16.5 years; mean Burke-Fahn-Marsden (BFM) 32.9±14.1) and 7 with CD (4 females; mean age, 46.2±9.8 years; mean BFM 10.4±4.4). Parameters included barycentre displacement length, volume, velocity, angular velocity and power spectral density (PSD) in low-frequency (delta and theta) bands. Dystonia severity was assessed using the BFM scale.Results In the pooled cohort, GPi-DBS significantly reduced dystonia severity, with mean BFM scores decreasing from 21.6±15.4 preoperatively to 14.1±13.1 postoperatively (p=0.011, permutation test). In subgroup analyses, BFM scores decreased significantly in the CD group (p=0.015), while a non-significant trend toward improvement was observed in the GD group (p=0.076). Kinematic analysis in the pooled cohort demonstrated a robust reduction in barycentre angular velocity (p<0.001), whereas other parameters were not significantly modified. In the CD subgroup, additional significant reductions were observed in displacement length, velocity and PSD amplitudes in both frequency bands (all p<0.01). Multivariate regression analysis demonstrated that kinematic improvements in barycentre displacement length, velocity, angular velocity and PSD in delta and theta bands were significantly associated with clinical improvements (all p<0.05).Conclusions 3D kinematic analysis provides objective biomarkers of GPi-DBS effectiveness in dystonia. Despite differing response patterns, kinematic features remain informative across phenotypes supporting their use in individualised outcome assessment.