A new variant of papillary carcinoma of the thyroid is analysed, known as 'diffuse sclerosing'. This lesion is characterized by a papillary cancer with a marked lymphocytic infiltration, intense fibrosis and a large number of psammoma bodies. Of a population of 158 differentiated thyroid carcinomas, we found four cases of this rare variant. The clinicopathological characteristics were studied together with the importance of an accurate diagnosis and prognosis, and the data obtained were compared with those of a 'well-differentiated or classical' papillary cancer, which yielded the following outstanding features: (a) younger age of presentation; (b) greater affinity for males; (c) greater frequency of extrathyroid extension; and (d) greater frequency of recurrences. The clinical importance of recognizing this variant is based on the need to apply a more aggressive treatment and a more exhaustive follow-up to such patients.