Background: Electroconvulsive therapy (ECT) is an effective treatment for depression with potential transient cognitive side effects. However, subjective memory impairment can extend over a long period after ECT. Objectives: This study aimed to assess potential risk factors for long-term subjective memory impairment 6 months after ECT and to explore if the associations are mediated by depressive symptoms. Methods: This registry-based study used the Swedish National Quality Register for ECT and other national registers. Long-term subjective memory worsening was defined as a minimum 2-step worsening on the memory item from the comprehensive psychopathological rating scale (CPRS-M) from before ECT to 6 months after ECT. Changes on the scale were also analyzed in continuous models. Statistical methods used were logistic regression and linear regression analyses in univariable and multivariable models. Results: The study population consisted of 1498 patients. Subjective memory worsening occurred in 25.2 % of the population. Long-term subjective memory worsening was associated with more depressive symptoms and lower education levels. No association could be found related to ECT technical factors. The associations between age and psychiatric comorbidities with subjective memory worsening were mediated by depressive symptoms. Conclusion: Patients can be informed that depressive symptoms are one of the biggest contributing factors to long-term subjective memory impairment after ECT. A successful treatment is therefore important to minimize the long-term experience of memory deficits. The number of sessions or ECT technical factors do not seem to be associated with long-term subjective memory impairment.