Lymphatic malformations that involve the nervous system are uncommon. The authors review their experience with involvement of the brachial plexus and its branches by cystic hygromas. A retrospective review of the authors' experience with pathology of the pediatric brachial plexus revealed 4 cases involving patients with compression of this structure and its branches due to cystic hygroma. Although such cases are apparently rare, the neurosurgeon should consider malformations of the lymphatic system in the differential diagnosis of masses involving the brachial plexus and its branches.