Background: Attention-deficit/hyperactivity disorder (ADHD) is common and may require treatment in adulthood. We aimed to investigate the treatment patterns and perinatal outcomes of women with any history of stimulant treatment for ADHD. Methods: We used health records of the New South Wales (NSW, Australia) population to compare perinatal outcomes of women treated with stimulants (dexamphetamine or methylphenidate) for ADHD from 1982 to 2012 who gave birth between 1994 and 2012, with perinatal outcomes of women with no known ADHD or stimulant treatment (comparison cohort). Five comparison women, matched by maternal age and infant year of birth, were selected for each treated woman. Pregnancy outcome odds ratios in the two groups were adjusted for confounders including maternal age and smoking. Results: Of 5056 women treated for ADHD with stimulant medication, 3351 (66.3%) had stimulant treatment documented before the index pregnancy but not within 1 year before the expected date of delivery, 175 (3.5%) had stimulant treatment before and possibly during pregnancy (stimulant prescription within the 12 months directly before the expected date of the index birth and earlier), and 1530 (30.2%) had no stimulant treatment until after the index pregnancy. Treatment for ADHD at any time (before, before and during and only after the index pregnancy) was associated with reduced likelihood of spontaneous labour—odds ratios (ORs) 0.7 [0.7, 0.8], 0.7 [0.5, 0.9], and 0.7 [0.7, 0.8], respectively—and increased risk of caesarean delivery (1.2 [1.1, 1.3], 1.3 [0.9, 1.8], 1.3 [1.1, 1.4]); active neonatal resuscitation (1.2 [1.0, 1.3], 1.7 [1.1, 2.7], 1.3 [1.0, 1.7]); and neonatal admission > 4 h (1.2 [1.1, 1.3], 1.7 [1.2, 2.4], 1.2 [1.0, 1.4]). Treatment before or before and during pregnancy was, in addition, associated with increased risk of pre-eclampsia (1.2 [1.0, 1.4], 1.5 [0.8, 2.6]); preterm birth < 37 weeks (1.2 [1.0, 1.3], 1.4 [0.9, 2.3]); and 1-min Apgar < 7 (1.2 [1.1, 1.3], 2.0 [1.4, 2.9]). Stimulant prescribing was low during pregnancy (3.5% of women received such a prescription) and dropped during the 12 months before the due date from an average of 24.7 prescriptions per month in the first 6 months to 4.5 per month in the final 6 months. Conclusions: Compared with no treatment, ADHD stimulant treatment at any time was associated with small increases in the risk of some adverse pregnancy outcomes; treatment before, or before and during pregnancy, was associated with additional adverse outcomes, even after a treatment-free period of several years. None of these associations can be confidently attributed to stimulant treatment; in all cases ADHD per se or correlates of it could be responsible for the association.