The CDC25 phosphatases are key regulators of normal cell division and the cell's response to DNA damage. Earlier studies suggested non-overlapping roles for each isoform during a specific cell cycle phase. However, recent data suggest that multiple CDC25 isoforms cooperate to regulate each cell cycle transition. For instance, although CDC25A was initially thought to exclusively regulate the G(1)-S transition, recent data demonstrate a significant role for CDC25A in the G(2)-M transition. Further evidence demonstrates that in addition to the ATM/ATR-CHK pathway, a p38-MAPKAP pathway is also involved in controlling CDC25 activity during G(2)/M checkpoint activation. Together with the fact that CDC25 overexpression is reported in many cancers, these data highlight the significance of developing specific CDC25 inhibitors for cancer therapy.