The purpose of this study was to assess the efficacy of the lactational amenorrhea method (LAM) for family planning among mothers who are separated from their infants by work. The study population, 170 urban middle class women who planned to return to work before 120 days postpartum, were interviewed monthly for 6 months postpartum and contacted at 12 months. The study population received clinical support for expressing their milk and exclusively breast-milk feeding the infants and for the use of LAM for birth spacing. The cumulative life table pregnancy rate by 6-month was 5.2%, with 3 pregnancies, one at each of months 4, 5, and 6. LAM for working women, as described in this article, might be associated with a higher pregnancy risk than LAM use among non-working women. Therefore, women using LAM should be informed that separation from the infant might increase their risk of pregnancy.