BACKGROUND Primary extranodal diffuse large B-cell lymphoma (DLBCL) is a rare, yet highly aggressive and invasive malignancy that can masquerade as a solid organ tumor. Timely diagnosis is critical for improving prognosis; however, it is challenging to achieve. CASE REPORT We report 2 cases treated at Yale New Haven Hospital (New Haven, CT, USA) and the West Haven Veteran's Affairs Medical Center (West Haven, CT, USA) in 2023. Case 1 describes a 69-year-old woman who presented with a large left adrenal mass that was suspicious for adrenocortical carcinoma and was found to have primary adrenal DLBCL following surgical resection. Case 2 describes a 59-year-old woman with Hashimoto's thyroiditis and goiter who was found to have primary thyroid DLBCL following partial thyroidectomy. CONCLUSIONS Primary extranodal DLBCL should be included in the differential diagnosis of solid adrenal and thyroid tumors. The risks of biopsy, given currently available techniques, should be weighed against the benefits of achieving a definite diagnosis, allowing for timely initiation of systemic immunochemotherapy. When biopsy can be safely performed, techniques designed to evaluate for DLBCL should be incorporated.