Background: Frequent hospital emergency department (ED) use has been increasing. The objective of this study is to analyze frequent ED use at a large NYC public hospital and to provide insight for effective intervention strategy development to reduce frequent ED use. Methods: A cohort of 775 (1% of all ED users, 11% of total ED use) frequent users with 10+ ED use per year was focused. Demographics, insurance, medical/mental problems and use of other hospital services were studied. Visual analytics was utilized for insight discovery and visualization. Result: 79% of this cohort were insured, 49% had primary care physicians but only visited once on average. Further break-down reveals different hospital service use patterns. Most also had higher utilization of acute and specialty clinics, while another group mainly utilized ED. More than half of the cohort suffer substance abuse and behavior health problems. Homeless had significant higher utilization of ED. The results reveal frequent ED users had unmet needs that could not addressed in other services but turned to ED for help. Conclusion: Analyzing determinants of individual health is essential for better understanding root causes of frequent ED use. Developing personalized intervention strategy is crucial to address those different unmet needs beyond scope of ED and healthcare services. Improving primary care access, health literacy education, collaborative partnership with other community and human services are crucial to reduce frequent ED use. The study also demonstrates visual analytics is an efficient approach to help care providers for insight discovery and effective strategy development.