This study examines the impact of the stress experienced by mothers during a child's cancer treatment. A descriptive correlation study has been designed to examine the relationships between uncertainty, sense of mastery, boundary ambiguity, and anxiety. The sample consists of 100 mothers recruited in two teaching hospitals in Taiwan. The sense of mastery was found to act as a mediator between uncertainty and anxiety, whereas uncertainty was a good predictor of boundary ambiguity. The first 2 months of treatment and the incidence of cancer recurrence represented a significant special experience for mothers. Nursing intervention to improve the mothers' sense of mastery and to assist families in establishing functional patterns of parent-child interaction is discussed.