Women diagnosed with breast cancer must make important surgical decisions. The decision-making process for younger women is complex, with this group more likely to have an advanced diagnosis and life-stage considerations that can impact on treatment. This study investigated the decision-making process of women aged <50 years who had undergone breast cancer surgery within the preceding 12 months in Aotearoa New Zealand. Twelve women participated in semi-structured qualitative interviews to explore the factors that influenced treatment decisions. Thematic analysis resulted in three themes. Fear was the main concept identified as the primary influence on initial decision-making. Good quality shared decision-making between patient and clinician was found to provide essential support during the diagnosis to treatment period. In addition, women expressed a need for multi-modal presentation of medical information and more material reflecting younger women. These findings inform provision for younger women making surgical decisions when diagnosed with breast cancer.