Multiple endocrine neoplasia type 1 (MEN 1) is a rare syndrome inherited in an autosomal dominant pattern, characterized by combinations of tumors of the parathyroid glands, pituitary gland, and pancreatic islet cells and more rare tumors of endocrine organs and nonendocrine tissues. Germline mutations in the MEN1 gene are responsible for the MEN 1 syndrome, leading to an inactive form of menin protein. Benign lesions of the parathyroid glands are characteristic in patients with the MEN 1 syndrome; however, patients can develop parathyroid carcinomas very rarely. This report presents a clinical case of the MEN 1 syndrome: a 39-year-old woman underwent surgery for carcinoma of two parathyroid glands as well as was treated for pituitary prolactinoma, which caused infertility, and malignant insulinoma; the patient had multiple subcutaneous lipomas as well. Genetic analysis revealed a novel germline mutation in the MEN1 gene - a nucleotide insertion at codon 43 in exon 2 (c.129insA), which caused the occurrence of the MEN1 syndrome. The clinical case of the MEN 1 syndrome presented here is relevant in gathering the data on etiopathogenesis of not only MEN 1 syndrome, but an extremely rare pathology - parathyroid carcinoma - as well.