Objective: To determine whether certain medication use during pregnancy is associated with restless legs syndrome (RLS). Design, Setting, Participants: A secondary analysis of a cohort study of first-time pregnant individuals enrolled at 8 U.S. sites between 10/1/2010 and 9/30/2013. Main Outcome Measures: RLS symptoms were ascertained in early (6 ⁰-13 ⁶) and mid (22 ⁰-29 ⁶) pregnancy based on the International RLS Study Group diagnostic criteria. Methods: Throughout their pregnancy, participants reported all medications taken. In early and mid-pregnancy, we created a set of dichotomous variables to indicate whether participants took any ‘at-risk’ medication from the 5 pre-specified categories, including first-generation antihistamines, serotonergic antidepressants, dopamine antagonists, tricyclic antidepressants, and mirtazapine. We estimated the relative risks of RLS symptoms by each category of medication use using Poisson regression, adjusting for age, race and ethnicity, and tobacco use. Results: Of 8,390 participants (27.2±5.6 years), 11.9% and 8.6% took ‘at-risk’ medications in early and mid-pregnancy, respectively. The most frequent medications were first-generation antihistamines and serotonergic antidepressants. The prevalence of RLS symptoms was 17.8% in early pregnancy and 30.0% in mid-pregnancy. Participants taking first-generation antihistamines (aRR [95% CI], 1.28 [1.08-1.53]) or serotonergic antidepressants (aRR [95% CI], 1.81 [1.53-2.14]) were more likely to experience concurrent RLS symptoms in early pregnancy. These associations were weaker in mid-pregnancy. Conclusions: The use of first-generation antihistamines and serotonergic antidepressants is prevalent in pregnancy and is associated with a higher prevalence of RLS symptoms. Awareness of this association may help both pregnant people and their clinicians make individualized decisions regarding medication use.