Population-level studies investigating the incidence of memory complaints during the COVID-19 pandemic are scarce. Objective: This study aimed to examine the incidence of memory complaints over 15 months during the COVID-19 pandemic in adults from Southern Brazil. Methods: Data from the PAMPA (Prospective Study about Mental and Physical Health in Adults) cohort, a longitudinal study with adults residing in Southern Brazil, were analyzed. An online-based, self-administered questionnaire was used to assess self-rated memory. Participants rated their memories as excellent, very good, good, fair, or poor. Incident memory complaints were defined as worse memory perception from baseline to follow-up. Cox proportional hazard models were used to identify factors associated with the increased risk of memory complaints. Results: During follow-up, a cumulative incidence of 57.6% for memory complaints was observed. Female sex (hazard ratio [HR] 1.49; 95% confidence intervals [CI] 1.16–1.94), lack of access to prescribed medicine (HR: 1.54; 95%CI 1.06–2.23), and worsened anxiety symptoms (HR: 1.81; 95%CI 1.49–2.21) were associated with an increased risk of memory complaints. Regular practice of physical activity was associated with a reduced risk of memory complaints (HR: 0.65; 95%CI 0.57–0.74). Conclusion: Since the COVID-19 pandemic, 6 in 10 adults in Southern Brazil have developed memory complaints. Factors including sex and lack of medications increased the risk of incident memory complaints. Physical activity reduced the risk of incident memory complaints during the COVID-19 pandemic.