Background: Primary dystonia is conventionally considered as a motor disorder, though an emerging literature reports associated cognitive dysfunction. Objectives: Here, we conducted meta-analyses on studies comparing clinical measures of cognition in persons with primary dystonia and healthy controls (HCs). Methods: We searched PubMed, Embase, Cochrane Library, Scopus, and PsycINFO (January 2000–October 2020). Analyses were modeled under random effects. We used Hedge's g as a bias-corrected estimate of effect size, where negative values indicate lower performance in dystonia versus controls. Between-study heterogeneity and bias were primarily assessed with Cochran's Q, I2, and Egger's regression. Results: From 866 initial results, 20 studies met criteria for analysis (dystonia n = 739, controls n = 643; 254 effect sizes extracted). Meta-analysis showed a significant combined effect size of primary dystonia across all studies (g = −0.56, P < 0.001), with low heterogeneity (Q = 25.26, P = 0.15, I2 = 24.78). Within-domain effects of primary dystonia were motor speed = −0.84, nonmotor speed = −0.83, global cognition = −0.65, language = −0.54, executive functioning = −0.53, learning/memory = −0.46, visuospatial/construction = −0.44, and simple/complex attention = −0.37 (P-values <0.01). High heterogeneity was observed in the motor/nonmotor speed and learning/memory domains. There was no evidence of publication bias. Moderator analyses were mostly negative but possibly underpowered. Blepharospasm samples showed worse performance than other focal/cervical dystonias. Those with inherited (ie, genetic) disease etiology demonstrated worse performance than acquired. Conclusions: Dystonia patients consistently demonstrated lower performances on neuropsychological tests versus HCs. Effect sizes were generally moderate in strength, clustering around −0.50 SD units. Within the speed domain, results suggested cognitive slowing beyond effects from motor symptoms. Overall, findings indicate dystonia patients experience multidomain cognitive difficulties, as detected by neuropsychological tests. © 2022 International Parkinson and Movement Disorder Society.