Treatment with immune checkpoint inhibitors (ICI) has expanded into the adjuvant setting enhancing the importance of knowledge on the immune-related toxicities and their impact on health-related quality of life (HRQoL). Large phase 3 trials of patients with resected Stage III/IV melanoma found no effect on HRQoL during adjuvant immunotherapy. This study investigates how HRQoL was affected during and after adjuvant immunotherapy in a real-world setting. Patients with resected melanoma treated with adjuvant nivolumab from 2018 to 2021 in Denmark were identified using the Danish Metastatic Melanoma Database (DAMMED). The study was performed as a nationwide cross-sectional analysis as a questionnaire consisting of six different validated questionnaires on HRQoL, cognitive function, fatigue, depression, fear of recurrence, and decision regret was sent to all patients in March 2021. To evaluate HRQoL during and after adjuvant treatment, patients were divided into groups depending on their treatment status when answering the questionnaire; patients in active treatment for 0–6 months, patients in active treatment for >6 months, patients who ended treatment 0–6 months ago, and patients who ended treatment >6 months ago. A total of 271/412 (66%) patients completed the questionnaire. Patients who ended therapy 0–6 months ago had the lowest HRQoL and had more fatigue. Patients in active treatment for >6 months had lower HRQoL and more fatigue than patients who started treatment 0–6 months ago. Patients ending therapy >6 months ago had higher HRQoL and less fatigue compared to patients who ended therapy 0–6 months ago. Multivariable analysis showed an association between HRQoL and treatment status, comorbidity, civil status, and employment status. Adjuvant nivolumab may affect some aspects of QoL, but the influence seems temporary. Patient characteristics, such as civil status, employment status, and comorbidity were associated with HRQoL.