Despite the interest of researchers in IgG4‐related disease (IgG4‐RD), many questions still remain unanswered regarding the thyroid gland. We aimed to clarify the relationship between IgG4‐positive plasma cells and the histopathological pattern in the Hashimoto thyroiditis (HT) in a Finnish series. HT specimens (n = 280) were retrieved from the Department of Pathology, Fimlab Laboratories. After re‐evaluation, 82 (29%) cases (72 females and 10 males, 52 ± 17 years) with significant fibrosis were selected. CD38, IgG and IgG4 positivity in plasma cells was evaluated by immunohistochemistry. Adjusted IgG4‐positive plasma cells per HPF > 20 and IgG4‐ to IgG‐positive plasma cell ratio > 30% were adopted as threshold criteria and related to other morphological features. IgG4‐positive HT group included 13 cases (15% from fibrotic HT, 4.6% from all HT, 50 ± 15 years, 11 females) with adjusted HPF count 30 ± 5 (23–40) IgG4‐positive cells. IgG4‐positivity significantly correlated with the presence of lobulation, oncocytic metaplasia and certain type of fibrosis, fibrosis spread outside the gland, lymphocytes/plasma cells epithelial penetration, the predominance of microfollicles and follicular atrophy in the present study. Despite the persisting uncertainty whether HT is IgG4‐RD, HT with IgG4‐positive plasma cells is histopathologically distinct entity with some geographic variability.