objective: to determine the effects of lead exposure on the time elapsed to become pregnant. material and methods: the study population consisted of 142 women residing in mexico city between 1997 and 2001, who were already participating in a study to evaluate effects of lead exposure on reproductive health. measurements of lead in bone were performed when women were first admitted to the program. information on lead exposure and other variables of interest was obtained through a questionnaire. participants were followed up to assess the relationship between the time required to become pregnant and lead exposure. statistical analysis consisted of kaplan-meier estimates and cox proportional hazards models. results: of the total number of women in the program, 42 got pregnant: 34 before the first year of follow-up, and 8 at a later date. the mean value for lead concentration in blood was 9.3 μg/dl. the mean values for lead concentration in patella and tibia were 16.0 y 11.0 μg pb/g of bone, respectively. survival analysis was performed and no differences were detected in blood lead levels and time to pregnancy in the first year. nevertheless, in women with blood lead levels above 10.0 μg/dl, the likelihood of not achieving pregnancy was five times higher (95% confidence interval [ci] 0.05-0.56) after one year of follow-up compared with women with blood lead levels below 10.0 μg/dl. conclusions: exposure to high lead concentrations may be an important risk factor influencing the time period for a woman to get pregnant, especially in fertile women who have tried to get pregnant for more than a year.