The smear histories of 312 women with cancer of the cervix have been determined. Eighty nine women had had at least one negative smear reported in the 10 years before a diagnosis of cancer and 14 had had more than one negative smear. Fifty six of the 89 women had had a negative smear in the three years preceding the diagnosis of cancer. The highest number of negative smears (61) reported was among the 115 women aged under 45. Fifty eight slides reported as negative were submitted to independent review; 13 were subsequently reported as negative, 11 as unsatisfactory, and 34 as abnormal. These findings may in part explain why in this region there has been a disappointing reduction in the incidence of clinically invasive cervix cancer, and our findings may also apply elsewhere. Nevertheless, the confirmed negative smears chiefly occurred within three years of clinical cancer, particularly in the younger women, and this finding suggests that these women may have a short preinvasive phase.