On the morning of December 26th, 2004, at least 280,000 people lost their lives to the largest Tsunami ever recorded. Relative to other natural disasters, little is known about the patterns of health service utilization following a tsunami. In a prospective cohort study, we described the patterns of health service utilization in four Tsunami-affected provinces (Phuket, Phang Nga, Krabi, and Ranong), one and two years post-Tsunami in Thailand. There were two study groups: 1) tsunami-affected (N=1,035) and 2) unaffected participants (N=854). We interviewed participants on their use of health services (i.e., outpatient services, inpatient services, home visits, medications, and informal care). The pattern of health service use varied for each service examined and at each of the two follow-up periods. Understanding the patterns of health service utilization may inform decision-makers and assist in future planning of post-disaster support. Often, organizations and governments fail to anticipate lasting effects of disasters and prematurely withdraw support services even though affected areas need long-term support.