Programmed cell death (apoptosis) is a conserved, natural mechanism for the removal of redundant and unwanted cells during normal development. This article reviews the evidence that apoptosis may also control the response of tumor cells to treatment with cytostatic drugs. Whereas most clinically used anti-cancer drugs can activate late events of apoptosis (DNA degradation and morphological changes) there are differences in essential signalling pathways between pharmacological cell death and the physiological induction of an active suicide programme. However, deregulation of normally integrated cell cycle progression appears a central signalling event in most forms of apoptosis, linking cell cycle control, DNA repair and cell death. Whether apoptosis is the cause or the consequence of drug-induced cell death remains to be established.