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Immunoglobulin G4-related disease (IgG4-RD) is a chronic inflammatory condition that has been suggested to increase cancer risk, but the incidence and types of associated malignancies remain unclear. This study aimed to evaluate the cancer risk in patients with IgG4-RD using a nationwide population-based cohort. We identified 2,150 patients newly diagnosed with IgG4-RD between January 2012 and December 2020 from the Korean National Health Insurance Service database. Patients were followed until the occurrence of cancer, death, or December 31, 2021. Standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) were calculated to compare cancer incidence in IgG4-RD patients with that in the general population. Subgroup analyses were conducted based on sex, age at diagnosis, follow-up duration, and use of immunosuppressive agents. Patients with IgG4-RD had a significantly increased risk of overall cancer (SIR 4.12, 95% CI 3.48-4.85), including solid tumors (SIR 3.33, 95% CI 2.74-4.02) and hematologic malignancies (SIR 15.31, 95% CI 10.17-22.13). Among solid tumors, the highest risks were observed for pancreatic cancer (SIR 14.54, 95% CI 8.31-23.62), central nervous system cancer, and biliary tract cancer. Myelodysplastic syndrome and non-Hodgkin lymphoma were the most frequent hematologic cancers. Cancer risk was higher in female patients. The risk peaked within the first year after IgG4-RD diagnosis (SIR 7.13, 95% CI 5.65-8.89). Patients with IgG4-RD have a significantly elevated risk of developing cancer, particularly myelodysplastic syndrome, non-Hodgkin lymphoma, pancreatic cancer, and biliary tract cancer. Close surveillance for malignancy is warranted, especially during the first year after diagnosis.