Sample size considerations A total of 366 couples will be randomized to the two arms within strata defined by whether this is their first pregnancy. The primary objectives are to test whether there are arm differences in the proportion of fathers who are abstinent from smoking at 28 weeks of pregnancy (time 1) and at 12 months post-randomization (time 2). We expect attrition rates among fathers of 20% and 30% at time 1 and time 2, respectively; dropouts will be imputed to be non-abstinent in an intention-to-treat analysis. The chi-square test for a difference in two proportions will be used to test the null hypotheses of no difference in abstinence rates between the two arms. The overall one-sided alpha level will be controlled at 0.025 by conducting each test at a one-sided alpha of 0.0125. Based on Nevid and colleagues' previous study that compared counseling to pamphlets,[Nevid, 1997] we anticipate abstinence rates of 10% and 5% in the Guia only arm at time 1 and time 2, respectively. The alternative hypotheses are that the arm difference at time 1 will be 15% (25% versus 10%) and at time 2 will be 10% (15% versus 5%). A sample of size 366 was selected to have at least 90% power for each alternative hypothesis. For the effect at time 2 to have 90% power, the effect at time 1 is overpowered at 97%. It is assumed that the arm effects of 25% versus 10% at time 1 and of 15% versus 5% at time 2 consider those participants who dropout and have their outcomes imputed to be non-abstinent. Thus, under the alternative hypotheses, the probabilities of response among just those 80% and 70% who do not drop out are (31% versus 13%) and (21% versus 7%), respectively.