BACKGROUND: Restless legs syndrome (RLS) is characterized by sensorimotor symptoms that usually are localized in both legs, but may present considerable asymmetry. Patients with strictly and persisting unilateral manifestations have not yet been reported. METHODS: We describe the clinical and electrophysiological characteristics of three RLS patients with unilateral symptoms. RESULTS: All essential RLS criteria were fulfilled in each patient. Neuroimaging and electrophysiological studies did not reveal structural lesions. All patients showed a predominance of periodic limb movements in sleep (PLMS) ipsilaterally to the RLS symptoms. Treatment response to dopaminergic drugs was favourable only in one patient. CONTROLS: Our observations suggest the existence of unilateral RLS with predominantly ipsilateral PLMS as a (so-far unrecognized) variant of RLS.