The reported prevalence of autism spectrum disorder (ASD) has more than tripled in the past two decades in the United States, due in part to improved screening and diagnostic techniques. Epidemiologic data on ASD, however, are largely limited to population-based surveillance systems. We examined epidemiologic patterns in ASD diagnoses among inpatients aged 1-20 years, using data from the Kids' Inpatient Database (KID) from 1997 to 2019. ASD cases were identified using ICD-9-CM and ICD-10-CM codes. Of 9,267,881 hospital discharges studied, 110,090 (1.19%) had a diagnosis of ASD. The prevalence of ASD was higher among males compared to females (1.53% vs. 0.54%) and was highest among non-Hispanic Whites (1.28% vs. 0.95% in non-Hispanic Blacks, 0.94% in Hispanics, and 1.18% in Other races). ASD prevalence increased from 0.18% to 1997 to 3.36% in 2019 (Z= -273.40, p < 0.001). The absolute increase was higher among males compared to females (0.26-4.90% vs. 0.08-1.77%) and among non-Hispanic Whites (0.18-2.88%) compared to non-Hispanic Blacks (0.23-2.72%), Hispanics (0.14-2.60%), and Other races (0.19-2.97%). The epidemiologic patterns of ASD based on inpatient data are generally consistent with reports from the community-based autism surveillance system. Our findings indicate that KID and other health services data might play a complementary role in ASD surveillance.