The restless legs syndrome (RLS) and periodic limb movement disorder (PLMD) are distinguishable but overlapping disorders. Both feature nocturnal involuntary limb movements (periodic limb movements) that can cause sleep disruption, but each has distinct clinical features that are relevant to the diagnosis and management of the patient. The diagnosis of RLS is made by meeting established clinical criteria, not from discovery of periodic limb movements of sleep (PLMS) on a sleep study. PLMD, however, does require the presence of PLMS on polysomnography as well as an associated sleep complaint. Moreover, PLMS are themselves nonspecific, occurring both with RLS and with other sleep disorders as well as in normal individuals. The diagnosis of PLMD, then, requires not merely finding a significant number of PLMS but also excluding other potential causes for the associated sleep complaint. Treatment of RLS is based on consideration of the pattern and severity of the disorder, with dopaminergic drugs generally favored for initial treatment. Anticonvulsants, opioids, and sedative/hypnotics also have a role. A treatment algorithm is provided to assist with the management of RLS. Treatment of PLMD relies on many of the same medications, but is generally more straightforward and places a greater reliance on levodopa compounds and sedative-hypnotics.