Periodic leg movements in sleep (PLMS) unrelated to restless legs syndrome (RLS) are a polysomnographic finding with a controversial clinical value. We describe a patient with isolated periodic leg movements in sleep (without any awake or sleep complaints), who developed severe diurnal RLS symptoms a few months after starting dopaminergic treatment, a phenomenon mimicking augmentation. The diurnal RLS symptoms disappeared after withdrawal of the dopaminergic drugs. Serum ferritin levels were relatively low (31-61 mcg/l; normal: 30-400 mcg/l). Since low levels of ferritin have been implicated in the genesis of RLS, and augmentation is a phenomenon associated with RLS, our findings here suggest that asymptomatic PLMS may have pathogenic mechanisms similar to RLS. Isolated PLMS and RLS could be, at least in some cases, different clinical forms of the same disorder. The conjunction of dopaminergic treatment with low ferritin levels may expose a patient with isolated PLMS to the development of RLS. Discontinuation of dopaminergic drugs in patients with isolated PLMS who develop RLS during the course of the treatment would be a reasonable recommendation.