Background and Objectives Overweight and obesity in pregnant women are a growing problem contributing to increased risks of obstetric and perinatal complications. However, the impact of maternal overweight and obesity on the risk of perinatal stroke in the infant remains unexplored. We aimed to evaluate the association between maternal early pregnancy body mass index (BMI) and risk of perinatal ischemic stroke. Methods This nationwide cohort study includes singleton births in Sweden at >= 22 + 0 weeks without major congenital malformations, between January 1, 1998, and December 31, 2019, with a follow-up time of up to 28 days after birth. Data were obtained by individual record linkages of nationwide Swedish registers. Exposure was maternal BMI in early pregnancy. The outcome, perinatal ischemic stroke, was defined as a diagnosis of ischemic stroke at <= 28 days of age in the Medical Birth Register, the National Patient Register, or the Swedish Neonatal Quality Register. Multivariable Poisson log-linear regressions and spline regression were used to estimate adjusted rate ratios (aRRs) and 95% CIs. Results Among the 2,140,852 births, 415 infants (192 girls) were diagnosed with perinatal ischemic stroke. Rates of perinatal ischemic stroke increased from 19/100,000 in infants to normal-weight women (BMI 18.5 < 25 kg/m(2)) to 22/100,000 among infants to mothers with overweight (BMI 25 < 30 kg/m(2)), to 35/100,000 among infants to women with obesity class II (BMI 30 < 35 kg/m(2)), and to 40/100,000 among infants to women with obesity class III (BMI >= 35 kg/m(2)). The adjusted rate ratio of perinatal ischemic stroke increased almost linearly with increasing maternal BMI. When estimating risk per BMI class, aRRs of perinatal ischemic stroke were 1.16 (95% CI 0.91-1.46) for overweight, 1.82 (95% CI 1.34-2.44) for obesity class I, and 1.96 (95% CI 1.27-2.91) for obesity classes II-III, compared with infants of mothers with normal weight. Discussion The risk of perinatal ischemic stroke increased with increasing maternal BMI in a dose-response manner. The findings support maternal obesity as a potential risk factor of perinatal ischemic stroke. A limitation of this study was that although the perinatal ischemic stroke diagnosis has high predictive value in Swedish registers, we cannot rule out that cases might be underdetected.