The oncogenic potential of the transcription factor c-MYC is well-established. Far less appreciated is the vital supporting role of MYC’s relative MNT. Using MYC transgenic mouse models, we have found that MNT enhances the survival of MYC-driven lymphoid cells and that, in its absence, the premalignant pool is markedly reduced and lymphomas fail to develop. Our evidence indicates that MNT protects normal and MYC transgenic B and T lymphoid cells from apoptosis by suppressing expression of the BH3-only protein BIM, a major trigger for apoptosis. Our results suggest that MNT may be an important new drug target for B and T lymphoid malignancies.