Three cases of Riedel's thyroiditis are reported. The clinical presentation varied, with thyroid nodule in 2 cases (associated with cervical lymph node enlargement in 1 case) and compressive goitre with mediastinal involvement in the third case. The histological diagnosis of Riedel's thyroiditis is difficult and was made retrospectively in these 3 patients; it is based on the absence of malignant cells and the presence of fibrosis, inflammatory infiltrates and, inconstantly, vascular lesions of the occlusive phlebitis type.