Aims Our aim was to examine intellectual development in children with congenital hemiplegia from early childhood to adolescence. Method Full-scale IQ (FIQ), Verbal IQ (VIQ), and Performance IQ (PIQ) scores were measured in 32 participants (19 males, 13 females) with congenital hemiplegia at mean ages of 4 years 6 months (SD 7mo; 31 participants), 7 years (SD 6mo; 23 participants), and 14 years (SD 1y 5mo; 26 participants). Results The FIQ and VIQ scores did not change with age, but the PIQ declined significantly (0.7 points per year; p=0.004). The estimated mean (95% confidence intervals) scores in males born at term with right-sided lesions without epilepsy were FIQ 106.5 (95.29-117.74), VIQ 105.9 (95.57-116.24), and PIQ 103.7 (93.19-114.31). Those means were negatively associated with preterm birth. PIQ was negatively associated with epilepsy. VIQ increased more quickly in males and in children with right-sided lesions. Interpretation The results confirm previous findings of FIQ stability, PIQ decline, the impact of epilepsy, and the status of females with left-sided lesions, and also reveal the effect of gestational age at birth. They underline the importance of management focused on nonverbal functions and further the debate about the early lateralization of language, the 'crowding effect', and the difference in brain plasticity between males and females.