Aim : We explored the psychometric properties of the recently developed Tyneside Pegboard Test (TPT) for unimanual and bimanual dexterity in children with unilateral cerebral palsy (CP) and investigated the impact of sensorimotor impairments on manual dexterity. Method : In this cross-sectional study, the TPT was assessed in 49 children with unilateral CP (mean age 9y 8mo, SD 1y 11mo, range 6–15y; 30 males, 19 females; 23 with right unilateral CP). All participants additionally underwent a standardized upper limb evaluation at body function and activity level. We investigated: (1) known-group, concurrent, and construct validity and (2) impact of sensorimotor impairments including spasticity, grip force, stereognosis, and mirror movements using analysis of covariance, Spearman’s rank correlation (r), and multiple linear regression (R2) respectively. Results : TPT outcomes significantly differed according to the Manual Ability Classification System (p<0.001, known-group validity). Relationships were found between the unimanual TPT tasks and the Jebsen-Taylor Hand Function Test (r=0.86–0.88, concurrent validity). Bimanual TPT tasks were negatively correlated with the Assisting Hand Assessment, ABILHAND-Kids, and Children’s Hand-use Experience Questionnaire (r=−0.38 to −0.78, construct validity). Stereognosis was the main determinant influencing all tasks (p<0.001, R2=37–50%). Unimanual dexterity was additionally determined by grip strength (p<0.05, R2=8–9%) and mirror movements in the more impaired hand (p<0.05, R2=4–8%). Bimanual dexterity was also explained by mirror movements in the more impaired hand (p<0.01, R2=10–16%) and spasticity (p=0.04, R2=5%). Interpretation : The TPT is a valid test to measure unimanual and bimanual dexterity in unilateral CP. The results further emphasize the importance of somatosensory impairments in children with unilateral CP.