OBJECTIVES: This study was performed in order to delineate whether the onset of symptom onset follows circadian rhythm and to identify potential clinical characteristics with similar circadian distribution as that of symptom onset time in stroke patients. METHODS: We retrospectively analyzed the data of subjects who were registered in a prospectively collected stroke registry in Korea University Medical Center Anam Hospital from September 2007 to December 2013. A Cosinor analysis was used to examine the circadian variation of the symptom onset of stroke as well as various clinical parameters. RESULTS: A total of 2,047 patients with stroke were analyzed in our study. The Cosinor analysis showed significant circadian rhythm of stroke occurrence existed according to the symptom onset time of stroke (p<0.001) and the peak time for stroke occurrence was 12:22 (95% confidence interval 11:29-17:41). Cosinor analyses of other variables also showed significant circadian variation of age, fasting glucose, high-density lipoprotein (HDL), and low-density lipoprotein. The circadian distribution of low HDL was similar to that of stroke occurrence. CONCLUSIONS: The prevalence of stroke occurrence and low level of HDL peaked during the morning.