Objectives: It is uncertain if there are variations in the improvement of quality in life between sexes and age groups after electroconvulsive therapy (ECT). The aim of this study was to investigate how health-related quality of life changed after treatment and to examine differences in the results between sex and age groups. Methods: This register-based study used data from the Swedish national quality register for ECT. The study population was patients diagnosed with depression who had received ECT. Health-related quality of life was quantified using the 3-level version the EuroQol 5-dimensional questionnaire (EQ-5D 3 L). Analysis of variance was used to compare change in EQ-5D score from pretreatment to posttreatment between sex and age groups. Results: There was a statistically significant improvement in EQ-5D index score and EQ visual analog scale (VAS) score in all patient groups after ECT. The mean improvement in EQ-5D index score and EQ-VAS score ranged from 0.31 to 0.46 and 28.29 to 39.79, respectively. Elderly patients had greater improvement in EQ-5D index score and EQ-VAS score than younger patients. There was no significant difference in improvement between the sexes. The mean improvement in EQ-5D index score was 0.40 for male patients and 0.41 for female patients. Conclusions: Electroconvulsive therapy had a considerable effect on health-related quality of life in patients with depression of both sexes and all age groups. The improvement was greatest in elderly patients, who more often had psychotic features. More studies are needed to investigate the long-term effects of ECT and to further explain the varying treatment results between elderly and younger patients.