The G1/S transition in the cell cycle is one of the checkpoints that can be deregulated in tumor development potentially causing increased proliferation and impaired capacity to arrest genetically damaged cells. The balance between activating and inhibitory molecules acting in the check point area seems to be critical and overexpression of cyclins and/or downregulation of the cdk inhibitors have been observed in many malignancies including lymphomas. In this review we have focused on two of the interplayers in the G1/S transition namely cyclin E and p27, and present the current knowledge of aberrations affecting these proteins in lymphomas as well as associations with clinico-pathological data including survival.