The aim of this study was to describe health-related quality of life (HRQoL) and productivity in Dutch breast cancer patients treated with tamoxifen in an adjuvant setting. Patients who started treatment with a standard dose of tamoxifen and who gave written informed consent, were eligible for participation in this trial. A total of 145 patients were asked to complete a survey at 3 months (T1) and 6 months (T2) after initiation of tamoxifen. HRQoL was measured by the EQ-5D-5L and the FACT-B questionnaire, and productivity by using the iMTA Productivity Costs Questionnaire. At 3 months 137 (95%) and at 6 months 133 (92%) patients responded to the surveys. EQ-5D-5 L utility values for T1 and T2 were 0.81 ± 0.17 and 0.81 ± 0.18, respectively. FACT-B scores for T1 and T2 were 109 ± 17.9 and 108 ± 20.0, respectively. No differences in both EQ-5D-5 L utility and FACT-B scores were found between T1 and T2 (p > 0.05). Age and employment status were statistically significantly associated with FACT-B scores (p = 0.04 and p = 0.03, respectively), indicating that younger and unemployed respondents had lower FACT-B scores. Importantly, both short-term and long-term productivity improved during the first six months of tamoxifen treatment (p < 0.05). Here, short-term productivity losses (consisting of absenteeism, presenteeism and unpaid work) for T1 and T2 were estimated at € 855,- and € 396,-, respectively. Long-term productivity losses (consisting of absenteeism) for T1 and T2 were estimated at € 2876,- and € 1104,-, respectively. In conclusion, this study presents HRQoL scores using different instruments and detailed loss of productivity estimates for breast cancer patients treated with adjuvant endocrine therapy. The results presented here can be used to inform input parameters in health economic evaluations of interventions for patients with breast cancer in the Netherlands and other Western countries and ultimately support decision making.