To compare the clinical features, efficacy and safety of treatment regimens, and outcomes of childhood- and adult-onset Takayasu arteritis (TAK). The study was designed as a retrospective cohort study comparing patients with childhood-onset TAK (from 1986 onward) to patients with adult-onset TAK (from 1988 onward) who were followed up until 2014 or 2015 at 4 centers in Ontario, Canada. Demographic, clinical, laboratory, and angiographic features, treatment regimens, and outcomes were recorded throughout the course of the disease. Disease activity and damage scores were completed retrospectively. Twenty-nine children and 48 adults (median age at diagnosis 12.1 years and 31.2 years, respectively) were included. A lower predominance of females was observed among the childhood-onset TAK cohort (76% versus 100% of patients with adult-onset TAK; P < 0.01), and children had a shorter delay to diagnosis (median 6.0 months versus 12.2 months for adults; P = 0.03). The distribution of vascular involvement was also different, with children having significantly more aortic and renal artery involvement and a higher frequency of arterial hypertension. Relapses in the first year after diagnosis were common both in children (39%) and in adults (28%). Two children, but no adults, died. Childhood-onset TAK has a lower female predominance and a higher frequency of aortic and renal involvement compared to adult-onset TAK. Relapses and disease burden were high in both groups, corroborating the need for careful monitoring of disease activity and aggressive therapeutic management.