Significance Genetic defects in nuclear lamins or reduced expression of nuclear lamins is accompanied by nuclear blebs and an increased susceptibility for nuclear membrane ruptures. Nuclear membrane ruptures are exacerbated by subjecting cells to mechanical forces. Here, we demonstrate that cells lacking nuclear lamins have oblong nuclei, but no nuclear blebs and no protrusions of the chromatin beyond the bounds of the nuclear membranes. Nevertheless, the cells displayed frequent and prolonged nuclear membrane ruptures, associated with DNA damage and occasionally by cell death. Thus, the nuclear lamina is crucial for the integrity of the nuclear membranes and for limiting damage to DNA. We suspect that our observations could be relevant to disease caused by defects or deficiencies in the nuclear lamins.