Background: Women report their partner's smoking behaviour is critical to their own efforts to quit smoking during pregnancy, however little is known about the perceptions of their partners toward smoking in the context of their transition to fatherhood. The purpose of this study was to develop a theoretical explanation of the process of male partner smoking cessation during pregnancy. Method: Individual interviews were conducted with 23 rural, working-class men from Mid-Missouri, U.S.A. during pregnancy and post delivery. Constant comparative methods were used to collect and analyze data. Self-reported smoking status was verified by saliva cotinine analysis. Results: The transition to fatherhood motivated men to protect their babies from the effects of cigarette smoke. However, motivation, cessation goals and smoking behaviours changed during the course of pregnancy and post-delivery in response to men's growing awareness of fathering roles and responsibilities. Conclusions: Pregnancy can be considered an opportune timeframe to promote smoking behaviour change with men in the context of their transition to fatherhood. Implications: The primary focus of smoking behaviour interventions with fathers should encourage and support them to protect their babies from the effects of cigarette smoke. In addition, health professionals should be cognizant of men's individual perceptions of fathering roles and responsibilities during pregnancy to maximize their potential for smoking behaviour change. Although smoking cessation is an appropriate goal for fathers in early pregnancy, consideration should be given to encouraging harm reduction in the later stages of pregnancy and post delivery.