Background: The purpose of antenatal care is to improve pregnancy outcomernfor both the mother and the fetus. Antenatal care is more beneficial inrnpreventing adverse pregnancy outcomes when it is sought early in thernpregnancy and continued through to delivery. However, existing evidencernfrom developing countries including Ethiopia indicate that few women seekrnANC at early stage of their pregnancy.rnObjective: The objective of this study is to assess timing of fistrnantenatal care booking and factors that influence the timing.rnMethod: A cross sectional study design was used to collect data fromrn630 pregnant women who were attending antenatal care service at 10rngovernment health centers in Addis Ababa from March 1 to 30, 2008.rnResult: The proportion of respondents who made their first antenatal carernwithin the recommended time [before or at 12 weeks of gestation] was foundrnto be 40.2%. The timing of antenatal care booking ranges from 1st month torn9th months of gestation. The mean timing was 4 months [SD 1.8].rnMultivariate analysis revealed that respondents with parity zero, who saidrntheir pregnancy was planned and who received advice on advantage of earlyrnbooking were more likely to book timely compared to others [OR= 1.860, 95%rnCI: 1.005, 3.441], [OR=1.918, 95% CI:1.105,3.328] and [OR=10.236, 95%CI:rn4.580, 22.875] respectively. Past service utilization did not seen as predictorsrnfor timely booking.rnConclusions: Majority of pregnant mothers do not practice early booking ofrnantenatal care provided that the service is accessible. In order to improve thernsituation, implementation of focused antenatal care, clear guidelines for thernservice, and the need for training service providers are important.