Clinical studies are emerging which suggest that sex hormones may play a role in quit attempts and relapse. The present study aim is to determine if menstrual phase plays a role on a second self-selected quit attempt and subsequent relapse during a twenty-six week follow-up. Participants (n=138) were 29.7+/-6.5 years old and smoked 16.1+/-4.8 cigarettes per day. Participants were more likely to self-select a second quit date during the Follicular (F) phase (59.4%) than Luteal (L) phase (40.6%, p=0.033) and were also more likely to relapse during the F phase than the L phase (59.7% vs. 40.3%, p=0.043, respectively). Those who self-selected to quit in the L phase experienced a significantly longer time to relapse than those who chose the F phase (median of 3 days vs. 2 days, respectively; Hazard Ratio=1.599, p-value=0.014). This confirms previous work suggesting quit dates in the F phase are associated with worse smoking cessation outcomes. Additional research is needed to investigate how this relationship may vary with the use of pharmacotherapy.