AbstractCongenital Zika Syndrome (CZS) is characterized by many impairments especially in the central nervous system, potentially compromising neurodevelopment and causing significant morbidity in affected children. The aim was to assess gross motor function in children with CZS. This was a cross-sectional investigation nested within a prospective cohort study of children with CZS based in a Brazilian referral hospital in Rio de Janeiro. Between March/2017 and February/2018, we performed gross motor function assessments using the Gross Motor Function Classification (GMFCS) and the Gross Motor Function Measure (GMFM), estimating the mean and standard deviation of GMFM scores among GMFCS groups. The study sample included 72 children, with a median age of 13 months (7–25). Of these, 63 (87.5%) had severe motor impairment, 3 (4%) had moderate impairment, and 6 (8%) had mild impairment. The mean GMFM score for each group was respectively 11.6, 26.1, and 81.6, with statistically significant differences (p-value < 0.001). Severely affected children only achieved head control in the sitting posture when supported. Children with milder forms were able to develop walking skills.Conclusion: Most children with CZS have major motor disabilities and a poor prognosis. Better understanding of limitations and functionality in children with CZS can serve as a prognostic guide in their management. What is Known:• Severe motor impairment was present in 63 (87.5%) children with CZS.• The degree of neurological impairment was inversely associated with motor performance. What is New:• Microcephaly was more frequent among children with severe gross motor function impairment.• Children with CZS have major motor disabilities and a poor prognosis.