NK cells play critical roles in protection against haematological malignancies but can acquire a dysfunctional state, which limits anti-tumour immunity. However, the underlying reasons for this impaired NK cell function remain to be uncovered. We found that NK cells in aggressive B cell lymphoma underwent substantial transcriptional reprogramming associated with increased lipid metabolism, including elevated expression of the transcriptional regulator PPAR-g. Exposure to fatty acids in the lymphoma environment potently suppressed NK cell effector response and cellular metabolism. NK cells from both diffuse large B cell lymphoma patients and Eµ-myc B cell lymphoma-bearing mice displayed reduced IFN-g production. Activation of PPAR-g partially restored mitochondrial membrane potential and IFN-g production. Overall our data indicate that increased lipid metabolism, while impairing their function, is a functional adaptation of NK cells to the fatty-acid rich lymphoma environment.