Introduction The aim of this study was to evaluate the association of breast cancer with thyroid diseases. Many authors have already studied the possible relationship between these two diseases, but the results are nowadays conflicting. Materials and methods Our study examining 867 patients with breast cancer (862 women and 5 men, average age = 61 years old) of whom 141 also had thyroid disease evaluated the recurrence of thyroid diseases and their association with different types of breast cancer. Statistical analyses were performed using SPSS software for Windows; we used nonparametric tests (Chi-square and MannWhitney), and the level of significance was set at p < 0.05. Results We found a significant association between breast cancer diagnosed after menopause and thyroid disease (p < 0.003). Moreover, we analyzed the role of thyroid autoimmunity identifying an association between chronic autoimmune thyroiditis and breast cancer diagnosed before menopause (p < 0.05). Regarding receptor profile of breast carcinoma, we have found an increased expression of estrogen receptors in patients with autoimmune thyroiditis compared to patients with any other thyroid diseases (p < 0.03). Contrariwise, we do not have found any difference between the group with every thyroid disease and the group without thyroid disease (p < 1.00). We did not find other statistically significant associations with breast cancer's parameters like family history, tumor size, lymph node metastasis, distant metastasis, cancer clinical and pathological stage, differentiation grade and expression of Ki67, p53 and Her2 in the two main groups with or without thyroid disease. Likewise, we did not found other statistically significant association between hypothyroidism or hyperthyroidism and breast cancer.