P reclinical data support the potential of the death-signaling receptors for TRAIL as targets for cancer therapy. However, it is unclear whether these death-signaling receptors suppress the emergence and growth of malignant tumors in vivo. Herein we show that TNF-related apoptosis-inducing ligand receptor (TRAIL-R), the only proapoptotic death-signaling receptor for TRAIL in the mouse, suppresses inflammation and tumorigenesis. Loss of a single TRAIL-R allele on the lymphoma-prone Eμ-myc genetic background significantly reduced median lymphoma-free survival. TRAIL-R–deficient lymphomas developed with equal frequency irrespective of mono- or biallelic loss of TRAIL-R, had increased metastatic potential, and showed apoptotic defects relative to WT littermates. In addition, TRAIL-R^–/– mice showed decreased long-term survival following a sublethal dose of ionizing radiation. Histological evaluation of moribund irradiated TRAIL-R^–/– animals showed hallmarks of bronchopneumonia as well as tumor formation with increased NF-κB p65 expression. TRAIL-R also suppressed diethylnitrosamine-induced (DEN-induced) hepatocarcinogenesis, as an increased number of large tumors with apoptotic defects developed in the livers of DEN-treated TRAIL-R^–/– mice. Thus TRAIL-R may function as an inflammation and tumor suppressor in multiple tissues in vivo.