Background: Due to increased cardiometabolic risks and premature mortality in people with severe mental illness (SMI), monitoring cardiometabolic health is considered essential. We aimed to analyse screening rates and prevalences of cardiometabolic risks in routine mental healthcare and its associations with patient and disease characteristics. Methods: We collected screening data in SMI from three mental healthcare institutions in the Netherlands, using most complete data on the five main metabolic syndrome (MetS) criteria (waist circumference, blood pressure, HDL-cholesterol, triglycerides, fasting blood glucose) within a 30-day timeframe in 2019/2020. We determined screened patients' cardiometabolic risks and analysed associations with patient and disease characteristics using multiple logistic regression. Results: In 5037 patients, screening rates ranged from 28.8% (waist circumference) to 76.4% (fasting blood glucose) within 2019–2020, and 7.6% had a complete measurement of all five MetS criteria. Older patients, men and patients with psychotic disorders had higher odds of being screened. Without regarding medication use, risk prevalences ranged from 29.6% (fasting blood glucose) to 56.8% (blood pressure), and 48.6% had MetS. Gender and age were particularly associated with odds for individual risk factors. Cardiometabolic risk was present regardless of illness severity and did generally not differ substantially between diagnoses, in−/outpatients and institutions. Conclusions: Despite increased urgency and guideline development for cardiometabolic health in SMI last decades, screening rates are still low, and the MetS prevalence across screened patients is almost twice that of the general population. More intensive implementation strategies are needed to translate policies into action to improve cardiometabolic health in SMI.