Introduction: Multiple myeloma (MM) is a chronic malignant hematologic neoplasm characterized by the proliferation of clonal plasma cells¹. It is the second most common hematologic malignancy, accounting for 1–2% of all cancers and 2% of cancer-related deaths worldwide². With the introduction of new therapeutic options, five-year survival has increased, resulting in a larger proportion of patients exposed to the risk of developing multiple primary tumors (MPT)³?. Objectives: To assess the occurrence of multiple primary tumors among patients diagnosed with MM in Brazil between 1991 and 2021. Methods: This retrospective, descriptive study included patients diagnosed with MM (ICD-O-3 code 9732/3) and at least one additional primary neoplasm, excluding nonmelanoma skin cancer. Sociodemographic variables (sex, age, race/skin color, education, occupation, and region) and clinical characteristics (tumor site and date) were analyzed. Results: A total of 340 patients with multiple tumors were identified between 1991 and 2021. Most were male (53.2%), aged 60–69 years (31.8%), followed by those aged 70–79 years (30.9%). Only 11.8% were aged ≥80 years. The highest case frequencies occurred in Belo Horizonte (18.2%), Curitiba (12.4%), and Recife (9.4%). Whites represented 49.1% of cases and mixed-race individuals 29.7%. The most common tumor sites were prostate (n = 80), breast (n = 52), lower gastrointestinal tract (colon, rectum, anus; n = 28), melanoma (n = 26), and extramedullary plasmacytoma (n = 21). Synchronous tumors were more frequent in younger patients, with 55% occurring in individuals aged 0–59 years and none in those ≥80 years. Breast cancer (OR = 1.48; 95%CI: 0.67–3.39) and cervical cancer (OR = 1.80; 95%CI: 0.49–8.54) were more likely to occur after MM. Conclusion: Patients with MM exhibited a relevant occurrence of MPT, particularly prostate, breast, and gastrointestinal tumors, with increasing incidence among middle-aged women.