Abstract Objective This primary care study examined time trends in the incidence of anorexia nervosa (AN) and bulimia nervosa (BN) in the Netherlands across four decades. Methods A nationwide network of general practitioners, serving approximately 1% of the total Dutch population, recorded newly diagnosed patients with AN and BN in their practices from 1985 to 2019 (2,890,978 person‐years). DSM‐IV diagnostic criteria were consistently used and the same psychiatrist was responsible for the final diagnostic decision. Incidence rates (IRs) were calculated for: the total population (all ages), females overall, and females per 5‐year age category. Time trends in IRs were analyzed using JoinPoint regression analyses. Results In four decades, the incidence of AN among 10‐ to 14‐year‐old females increased significantly from 8.6 to 38.6 per 100,000 person‐years (average period percentage change [APPC] = 56.7; 95% confidence interval [CI] = 6.5–130.6. The overall incidence of AN was stable, with IRs ranging from 6.0 (95% CI = 4.3–8.1) to 8.4 (95% CI = 6.4–10.8). The IR of BN decreased significantly from 8.7 (95% CI = 6.7–11.0) to 3.2 (95% CI = 2.0–4.9) in the 2000s, before leveling off in the 2010s (IR 3.2; 95% CI = 2.0–4.8). Discussion The incidence of AN among 10‐ to 14‐year‐old girls increased significantly over four decades. Both biological and sociocultural factors, for example, early pubertal timing and the impact of social media, might explain this. In other age groups and overall, the incidence of AN remained stable. The significant decrease of the incidence of BN in the previous decades halted in the last decade. Public Significance An important finding of the present study is that for 10‐ to 14‐year‐old girls, the risk for developing anorexia nervosa has increased significantly over 40 years. More healthcare facilities for younger people are needed, and prevention programs could include social media use. For bulimia nervosa, the general decrease in the occurrence of new cases has halted in the 2010s.