OBJECTIVES: Individuals with cancer are at high risk for developing depression after cancer diagnosis. The risk of newly diagnosed depression can vary by cancer type due to differential survival prognosis. Therefore, the aim of this study was to examine the risk of newly diagnosed depression by cancer types (breast vs. female colorectal and prostate vs. male colorectal cancer) among elderly fee-for-service Medicare individuals with breast, colorectal and prostate cancer. METHODS: This study utilized a retrospective cohort study design using the Surveillance, Epidemiology and End Results (SEER)-Medicare data and consisted of 108, 640 elderly patients with incident breast, colorectal, and prostate cancer diagnosed from 2007 through 2011. This cohort was followed 12 months after the cancer diagnosis and newly-diagnosed depression was identified using the International Classification of Diseases-9^thEdition, Clinical Modification Codes during the follow-up period. Complementary log-log regression was used to examine the association between cancer type and depression diagnosis after adjusting for socio-demographics, access to care, chronic conditions, and cancer stage and cancer treatment. RESULTS: A significantly higher percentage of women with colorectal cancer developed newly-diagnosed depression as compared to women with breast cancer (5.50% vs. 3.62%), and a higher percentage of men with colorectal cancer developed newly-diagnosed depression as compared to men with prostate cancer (3.0% vs. 1.44%). In the adjusted analysis, women with colorectal cancer were at 41% higher risk to develop newly diagnosed depression as compared to women with breast cancer (adjusted risk ratio (ARR) = 1.41 [95%CI, 1.14-1.74]) and men with colorectal cancer were at 123% higher risk to develop newly diagnosed depression as compared to men with prostate cancer (ARR =2.23 [95% CI, 1.85-2.69]). CONCLUSIONS: The risk of newly-diagnosed depression varied by cancer type.