Cystic hygromas usually present in the first two years of life. We report a retrospective study of nine patients who first presented with neck and mediastinal masses after two years of age. The clinical evaluation of size, margins, and presence of respiratory symptoms can be used to select those requiring preoperative computed tomography. The five patients who had this examination all demonstrated mediastinal or axillary involvement. Patients in this older subset appear to be different from those presenting as infants because of the incidence of extension and the frequency with which disease is found outside of the posterior triangle.