The World Trade Center Health Registry (WTCHR), the largest post-disaster exposure registry in the United States, is a longitudinal study that tracks 71,000 enrollees to understand the long term health effects of the September 11 2001 terrorist attack. The baseline interviews were conducted during years 2003 and 2004, and a follow-up survey (Wave 2) was conducted during years 2006 and 2007. The third wave of the survey is currently underway and data collection will end in March 2012. In Wave 2, enrollees were offered web and mail modes throughout the survey. Phone interviews, due to its high cost, were only given as the last resort in the last 4 months of the 14-month data collection period. Wave 3 survey employs similar survey method to Wave 2. The objective of this paper is: 1) to understand what factors are related to enrollees’ choice of survey mode, particularly among Wave 2 phone participants; 2) to assess the interaction between survey reminders and mode preference. Our preliminary data show that, among enrollees who completed Wave 2 surveys by phone, 63% of them chose to complete Wave 3 by phone rather than by web or mail. Logistic regression on mode choice among this group found that: 1) the preference of phone over web is significant among older [Odds Ratio (OR) 0.24, 95% CI 0.07-0.08] and less educated people [OR 0.66, 95% CI 0.47-0.93]; and 2) the preference of phone over mail is significant among male [OR 0.71, 95% CI 0.50-0.95], Hispanic [OR 2.20, 95% CI 1.41-3.52], and low income groups [OR 2.21, 95% CI 1.10-4.51]. When data collection is complete, we will assess the interaction between survey reminders and mode preference. Results of this paper would help identify strategies to encourage survey participants to respond in less expensive survey modes without sacrificing response rate.