Bursts of cell proliferation after infection, injury or transformation can coincide with DNA damage and spindle assembly defects. These increase the risk of cell cycle arrest in mitosis, during which many cellular processes are uniquely regulated. Ultimately, cells arrested during mitosis may die, but adaptive mechanisms also allow their escape into the next interphase. This step can have variable consequences, including chromosome missegregation, polyploidization and centrosome amplification. Escaping cells can also initiate innate immune signalling, enter senescence or engage cell death, which in turn alert the microenvironment through nucleic acid sensing mechanisms and/or the release of danger-associated molecular patterns. Here we discuss the causes and consequences of deregulated mitosis and postmitotic cell fate, highlighting the impact of DNA damage repair, the spindle assembly checkpoint and extra centrosomes on genome integrity, as well as inflammatory signalling. Finally, we attempt to reconcile conflicting observations and propose variable modes that activate innate immune responses after mitotic perturbations.