To determine the prophylactic effect of using combined 1% alcoholic chlorhexidine gluconate and chlorhexidine gel-impregnated dressings (CGCD) on catheter-related thrombosis (CRT) in critically ill patients. This retrospective cohort study was performed in an intensive care unit from November 2009 to August 2014. The CRT incidence diagnosed with ultrasound examination was compared between patients applying CGCD and combined 10% aqueous povidone-iodine and standard transparent dressings (PITD) after central venous catheter insertion into the internal jugular vein for ≥ 48 h. CRT was stratified into early (within 7 days) and late (days 8-14) thromboses. Multivariate analyses using logistic regression models clarified the relationships between early- and late-CRT risks and skin antiseptic and catheter site dressing combinations. CRT occurred in 74 of 134 patients (55%), including 52 with early CRT and 22 with late CRT. Patients receiving CGCD had a significantly lower incidence of early CRT than those receiving PITD (odds ratio = 0.18; 95% confidence interval = 0.07-0.45, p < .001). No significant association was evident between using CGCD and late CRT (p = .514). Compared to PITD, CGCD reduced the CRT risk over 7 days in critically ill patients.UMIN Clinical Trials Registry: UMIN000037492.