Rationale:Primary lymphedema is a form of lymphedema marked by a dysfunction of the lymphatic system without preceding medical conditions. One rare subtype of primary lymphedema, lymphedema tarda, occurs in those older than 35 years and is difficult to diagnose. This paper reports 2 cases of unilateral lymphedema tarda in the lower extremities in South Korea.Patient concerns:The 2 patients complained of worsening swelling in the lower extremity for several months without any direct surgical or traumatic history related to the inguinal or lower extremity lymphatic system.Diagnosis:Primary lymphedema tarda may be determined by ultrasonography. Other vascular or infection-origin causes were excluded from further evaluations.Interventions:To confirm primary lymphedema tarda, lymphangiography was performed. In each case, lower extremity lymphangiography indicated dermal backflow and no lymph node uptake at the inguinal node of the affected side, which was compatible with lymphedema.Outcomes:The patients reported slight improvement in the symptoms after several weeks of rehabilitation.Lessons:This paper is the first report of the unilateral primary lymphedema tarda in South Korea. Further investigations are warranted to find the related etiology of this rare disease and a multimodality regimen is needed for improvement of symptoms.