['Augmentation is a major problem with dopaminergic therapy for restless legs syndrome (RLS), and predictors of augmentation have not yet been identified. We aimed to analyze the relationship between baseline ferritin level and occurrence of augmentation in a retrospective analysis of a prospective double-blind trial of cabergoline versus levodopa on augmentation in RLS.', 'Patients who experienced augmentation were compared to patients who did not experience augmentation.', 'Augmentation symptoms causing premature discontinuation from the study or which were tolerated (n=36, ferritin: 85+59 ng/ml) were associated with lower levels of serum ferritin compared to patients without augmentation (n=302, ferritin: 118+108 ng/ml, p=0.0062).'] Is augmentation in restless legs syndrome associated with low ferritin?