This multicenter study described the epidemiological characteristics, recorded first-ranked secondary diagnoses, and in-hospital burden of pediatric infectious mononucleosis (IM) hospitalizations in China during 2021-2023. Data were obtained from the FUTURE database. We identified hospitalizations with IM as the principal discharge diagnosis from discharge-record front pages at 31 tertiary children's hospitals between January 1, 2021, and December 31, 2023, and analyzed demographic, geographic, temporal, diagnostic, length-of-stay (LOS), and expense data using descriptive statistics and multivariable regression. Among 15,239 IM hospitalizations, representing 0.42% of all hospitalizations, the male-to-female ratio was 1.34. Children aged 4-6 years comprised the largest group, followed by those aged 1-3 and 7-12 years; 70.32% were urban residents, and admissions peaked in August and September. After adjustment for age, sex, seven-category geographic area, and month, the proportion of IM hospitalizations among all hospitalizations was lower in 2023 than in 2021-2022 (adjusted rate ratio, 0.822; 95% CI, 0.784-0.861; P < 0.001). A first-ranked secondary diagnosis was recorded in 68.29% of cases; bronchitis/pneumonia was the most common category, followed by hepatic dysfunction. Median LOS was 7 days, and median hospitalization expense was CNY 5,563.07. Encephalitis was recorded in only 15 cases but had the longest descriptive LOS and highest descriptive expenses. These findings provide a large multicenter baseline for the epidemiological patterns and in-hospital burden of pediatric IM hospitalizations across participating tertiary children's hospitals in China and may inform future surveillance and resource planning.
