Objective: To investigate the incidence and risk of renal-related complications in a nationwide cohort of Taiwanese patients with anorexia nervosa (AN). Method: This longitudinal cohort study analyzed the data of 43,951 individuals—comprising 2091 patients with AN and their controls matched (1:20) using propensity scores according to sex, age, degree of urbanization of residence, socioeconomic status, and year of diagnosis—from a population-based health insurance database; the study lasted 16 years. We used Kaplan–Meier curves to estimate the cumulative incidence of renal events. We also performed Cox proportional regression and constructed a risk model with death as a competing event (both adjusted for basic characteristics, renal diseases, and psychiatric comorbidities) to examine the risk of dialysis and renal outcomes in the AN group relative to the control group. Results: In total, 204 and 10 patients with AN had renal-related outcomes and end-stage renal disease (ESRD), respectively. The cumulative incidence rates of all renal outcomes and ESRD in the AN group were 10.72% and.64%, respectively, at 10-year follow-up. Compared with the control group, the AN group had a significantly higher risk of acute dialysis (adjusted hazard ratio 2.10 [95% confidence interval 1.19–3.68]), hypokalemia, hypovolemia, nephritis, acute renal failure, and chronic renal failure. The AN group did not have a significantly higher risk of ESRD. Discussion: The elevated risks of acute dialysis and some renal outcomes in AN highlight the importance of monitoring electrolyte imbalance and renal malfunctioning. Public Significance: Malnutrition and purging behaviors may cause renal complications in patients with AN. In this longitudinal cohort study, we found that the 10-year cumulative incidence of all renal outcomes in AN was 10.72%, and that patients with AN had a two-fold higher risk of overall renal outcomes compared with those without AN. Our findings imply that weight restoration and ceasing purging behaviors are crucial for recovery from AN.