Introduction: Heart Disease and Stroke Statistics_2014 Update suggests more than 424,000 people suffer out of hospital cardiac arrest (OHCA) in the United States. Hypothesis: We assessed seasonal variation in OHCA from a large national hospitalisation database in the past decade. Methods: The Nationwide Inpatient Sample database was used to estimate the annual number of hospitalisations with from 2000-2011. Identification of out of hospital cardiac arrest related hospitalisations was based on the designation of the International Classification of Diseases (9th Edition) Clinical Modification (ICD-9-CM) diagnosis code 427.5 (OHCA) as the principal discharge diagnosis. The frequency of hospitalisation for each month cumulative over 11 years was calculated and divided by number of days in that month to obtain the mean hospitalisations per day for each month. All calculations were carried out using the weighted estimates approximating nationwide population estimates. Results: An estimated 93,209 hospitalisations with primary diagnosis of OHCA occurred in the United States from the beginning of the calendar year 2000 to the end of the calendar year 2011. The number of hospitalisations per day in each month is shown in Figure 1.The number of hospitalisation was maximum in the winter months and minimum in summer months. Specifically, the mean number of hospitalisation each day (averaged over 11 years) was least in August (242). There was a rising trend from August to January. The average number of hospitalisation was highest in January (310); thereafter, the hospitalisation rate dropped to a nadir in August. There was however no seasonal pattern in inhospital mortality. Conclusions: We identified for the first time in United States an impressive pattern of seasonal variation in hospitalisations for OHCA. Further efforts must be made to identify triggers and methods to prevent OHCA and reduce its burden on health care system.