Background: The Rapid Assessment Disuse Index (RADI) is a brief tool aimed to promptly assess primary care patients' overall physical inactivity and sedentary behavior. This study examines the relation between physical inactivity and sitting time (RADI) to cardiometabolic risk among primary care patients. Methods: Survey data and electronic medical record information were collated to explore the association between RADI scores (cumulative and sitting) to metabolic syndrome (and components) among women and men, using multivariable logistic regression. Results: Among women, the cumulative RADI score was not significantly associated with metabolic syndrome. However, the RADI sitting score was related to low high-density lipoprotein cholesterol and metabolic syndrome. That is, a transition to a higher RADI sitting score by 1 unit (vs remaining in the score) was related with a 1.4 and 1.3 times higher odds for having low high-density lipoprotein cholesterol (95% confidence interval, 1.05-1.87) and metabolic syndrome (95% confidence interval, 1.02-1.64), respectively. Among men, no significant relations were found. Conclusions: The RADI sitting score is positively and significantly related to high-density lipoprotein and metabolic syndrome among women, yet not men. Due to the RADI's potential clinical utility, future research should attempt to examine these relations in larger, more robust samples and adjudicated outcomes using a prospective design.