Trials of adjuvant endocrine therapy for breast cancer have shown that aromatase inhibitors have little impact on global health-related quality of life (HRQoL), but have significant effects on patient-reported endocrine symptoms (ESs). There are few studies of HRQoL and psychological distress during preoperative endocrine therapy performed to determine endocrine responsiveness. The NEOS trial is a multicenter, phase 3 randomized controlled trial in postmenopausal women with hormone receptor-positive breast cancer. The primary aim of the trial was to evaluate the need for adjuvant chemotherapy in patients with clinical T1c-T2N0M0, hormone receptor-positive tumors who responded to neoadjuvant letrozole (LET) administered for 24-28 weeks before surgery. The primary endpoint was disease-free survival and the secondary endpoints included adverse events, HRQoL, and cost-effectiveness. In a HRQoL sub-study, subjects were assessed at baseline and 4 and 16 weeks after starting neoadjuvant LET, using the functional assessment of cancer therapy-breast and its ES subscale, and the hospital anxiety and depression scale. HRQoL and psychosocial distress were analyzed in the uncontrolled phase during 24-28 weeks of neoadjuvant LET therapy in the NEOS trial. From May 16, 2008, to December 14, 2011, 503 patients were recruited into the HRQoL sub-study. The full analysis set included 497 patients with a mean age of 63-years old. The questionnaire response rates at enrollment and 4 and 16 weeks were 94.4, 90.7, and 89.1 %, respectively. There were no significant changes in the FACT-G or B-trial outcome index over time, but the social and family well-being score and the ES subscale deteriorated significantly, and the number of patients with clinically significant hot flush increased significantly. Anxiety, depression, and emotional well-being improved significantly after neoadjuvant LET. Neoadjuvant endocrine therapy with LET had no impact on global HRQoL, but did influence endocrine-related symptoms such as hot flush. This study is registered as UMIN000001090.