Aim. The association between papillary thyroid carcinoma (PTC) and chronic lymphocytic thyroiditis (CLT) has been reported in literature. The aim of this study was to examine this association evaluating the lesser or greater neoplastic aggressiveness. Methods. One hundred and eighty-nine patients were examined from June 2004 to June 2007; they were divided into two groups: Group A included all the patients affected by FTC without CLT and Group B all the patients affected by PTC with CLT association. The surgical treatment was in all the patients the total thyroidectomy (TT). For the study age, sex, tumour features (dimensions, angioinvasion,capsular infiltration, multifocality and lymphnode metastases) were taken into consideration. The analysis was carried on with Student t test and chi(2) analysis (statistically significant P<0.05). Results. Group A included 117 patients; Group B 72 patients. No statistical difference in sex (P=0.989), age (P=0.480); tumour dimension (P=0.832). The capsular infiltration was present in 23 cases in Group A and 19 in Group B (P=0.368). The difference in average diameter was found to be 1.161 +/- 0.5812 and 1.485 +/- 1.082 cm in Group A and in Group B (P=0.290), respectively. The angioinvasion was found in 9 cases of Group A and in 3 cases in Group B (P=0.510). Multifocality was found in 35 patients in Group A and in 26 in Group B (P=0.469). Conclusion. The CLT may have only a minimum unpact in the development of the tumour. In this study the association does not modify the aggressiveness.