Restless legs syndrome (RLS) is a common neurological sleep disorder in adults characterized by the following diagnostic criteria: an urge to move that is usually associated with unpleasant sensations and symptoms that are worse at rest, relieved by movement, and most severe at night. The definite diagnosis of RLS in children is stricter and consists of self-description of leg discomfort or the presence of 2 of 3 supportive criteria combined with 4 essential criteria for diagnosis in adults. RLS in childhood has often been misdiagnosed as growing pains or a part of normal development. As a result, physicians have often missed the chance for proper management. We diagnosed a case of RLS in a 5-year-old boy presenting with growing pains, whose mother was found to have had RLS since childhood. We confirmed RLS by using a polysomnograph, in which the indices of periodic limb movement syndrome (PLMS) and periodic limb movement during wakefulness (PLMW) were recorded to be compatible with RLS criteria. The patient's ferritin level was low normal, and his symptoms improved after taking iron supplements.