An epidemiological case control study nested in the Early Cancer Detection program of the Health Ministry in Mexico City was carried out to evaluate the principal reproductive risk factors associated with uterine cervix cancer. Information from 12,741 gynecological cytologies reported to the National Cancer Registry, during the period between January 2 to March 31, 1987 was studied. In this population group the most important reproductive risk factors associated with uterine cervix cancer were: multiple births (seven or more births, OR = 3.24, IC 95% = 2.20-4.76), initiation of active sex life before 14 years (OR = 1.53, 95% IC = 1.13-2.08) and late menarche (in the group with menarche after 17 year of ages OR = 3.22, 95% IC = 1.06-9.77). In relation to the Early Cancer Detection program, an important number of women made use of the program when they showed symptoms. The prevalence among women who had at least one symptom was 43.09 per cent. Women with a tumor at the cervical level at the time of the cytology were 7.76 times more likely to have of uterine cervix cancer (95% IC = 4.84-13.15). Symptoms such as dysfunctional bleeding (OR 2.79, IC 95% = 1.90-4.12), metrorrhagia (OR 2.66, 95% IC 1.83-3.86) and bloody leukorrhea (OR 2.64, 95% IC 2.05-3.38) can be relevant findings in women at high risk. The attributable fraction of higher exposure in the presence of gynecological signs and symptoms is the cervical tumor, with 87.46 per cent.(ABSTRACT TRUNCATED AT 250 WORDS)