Patients (40) with pelvic masses were examined with ultrasound; surgical exploration subsequently revealed an ovarian teratoma. The echographic appearance of the lesions was extremely variable. Although a number of characteristic features of teratomas were described (axial location, solid mural component, acoustic shadow and hair/fluid level), these occurred only in a minority (17/40) of patients. When the clinical setting suggests an ovarian teratoma, the ultrasonographer should consider it regardless of the internal architecture and consistency of the mass.