Knowledge of medical care in US Immigration and Customs Enforcement (ICE) detention centers is limited. Reviews show high rates of preventable deaths while in detention due to substandard medical care within detention centers. To describe characteristics of medical emergencies at ICE detention centers in California. This cross-sectional study analyzed emergency medical services (EMS)-reported medical emergencies activated through 911 from January 1, 2018, to December 31, 2022, at 3 of the 5 ICE detention centers in California: Adelanto ICE Processing Center, Imperial Regional Detention Facility, and Otay Mesa Detention Center. Medical services requiring 911 activation. Data included the number of EMS-reported medical emergencies; ICE-reported medical emergencies; patient age and sex; and medical data in the EMS report, including primary symptom, EMS provider (emergency medical technician or paramedic) impression, vital signs, and interventions performed, using descriptive statistics. In this analysis of 3 detention centers with a mean daily census of 775 (range, 504-1001) individuals per center, there was a median of 68 (IQR, 10-88) EMS-reported emergencies per center per year for a total of 1224 emergencies. The EMS-reported emergencies involved 881 males (72%) and 338 females (28%) with a median age of 39.0 (IQR 30.0-49.0) years. The ratios of female-to-male EMS-reported emergencies were 0.51 (95% CI, 0.31-0.87) at Adelanto, 0.86 (95% CI, 0.31-2.43) at Imperial, and 1.60 (95% CI, 1.40-1.83) at Otay Mesa. Pregnancy-related emergencies accounted for 12.4% (42 of 338) of emergencies in females. A total of 357 individuals (29.2%) had at least 1 abnormal vital sign during their EMS encounter. Psychiatric emergencies comprised 48 EMS responses (3.9%), despite higher rates of ICE-reported psychiatric-related complaints. The median number of monthly EMS-reported emergencies across all 3 centers was 3 (IQR, 0-9) vs 4 ICE-reported emergencies (IQR, 1-15). In this study of medical emergencies at 3 of 5 ICE detention facilities in California, there were discrepancies in EMS vs ICE reported emergencies. The data suggested that vulnerable populations, such as pregnant women, had an increased number of medical emergencies, while individuals with psychiatric emergencies accounted for fewer reported emergencies. Based on these findings, emergency medical care provision in ICE detention centers requires increased transparency to ensure appropriate delivery of care.