With suicide ranking as a leading cause of death globally, identifying modifiable risk factors is crucial. Suicidal ideation (SI) is a significant precursor to suicide, and there is a growing interest in the role of cardiometabolic factors, particularly the cardiometabolic index (CMI), multiplying the triglyceride-to-high-density lipoprotein cholesterol ratio by the waist-to-height ratio, in mental health outcomes. Previous studies have shown a notable relationship among lipid abnormalities, elevated triglyceride levels, and depressive symptom severity, including SI. This research investigated the correlation between the CMI levels of adult Americans and SI, utilizing data from the National Health and Nutrition Examination Survey (NHANES) ranging from the years 2005 to 2018. After collecting data on demographics, physical examinations, and laboratory testing, multivariate logistic regression analysis was conducted to assess the relationship between CMI and SI while adjusting for relevant factors. The study, which enrolled 15,849 individuals exhibiting symptoms of SI, constituting 3.47% of the total, revealed a significant association between CMI levels and SI. A significant positive association was found between CMI and SI (adjusted OR = 1.07, 95% CI: 1.02-1.13, P = .0029). Moreover, a nonlinear relationship was identified between CMI and SI, characterized by an atypical inverted U-shaped curve with a breakpoint at approximately CMI = 2.08. Subgroup analysis revealed consistent findings across various demographic and clinical subpopulations. The findings of this study demonstrate a substantial correlation between elevated CMI levels and an increased incidence of SI within the US population. Early interventions targeted at individuals with elevated CMI levels, such as psychological support or lifestyle adjustments, may mitigate the risk of SI.