This study explored how mothers communicated with their young adolescent daughters about the high-stakes topic of sex, as well as more everyday topics, from a Self-Determination Theory perspective. Mothers and their 11- to 14-year-old daughters (44 dyads) participated in two conversations and reported on their experiences. In the everyday conversation, maternal autonomy support was positively related to daughters' experience, engagement, and desire for additional conversations. In the sex conversation, maternal structure was positively associated with daughters' engagement, experience, and desire for additional conversations. Mothers were less autonomy supportive in conversations about sex, as compared to everyday topics. Maternal perceptions of threat were associated with less autonomy support in both conversations and worry during the conversation was negatively associated with autonomy support in the everyday conversation, and with structure in the sex conversation. Implications for intervention are discussed. (Contains 4 tables.)