PP-30-078 Background/Aims: Devastating health effects from recent heat waves (eg, Chicago 1995, Europe 2003), and projected increase in frequency, duration, and severity of heat waves from climate change, highlight the importance of understanding the health effects of periods of extreme temperature. We analyzed all-cause mortality risk for heat waves in New York, NY (1987–2005) and investigated how health effects relate to heat waves. Methods: Heat waves were defined as periods of >2 days with temperature >95th percentile for 1 May–30 September. Using a generalized additive model, we estimated the relative risk during each heat wave compared to non-heat wave days, controlling for other factors (eg, day of the week, time trends). We combined individual heat wave effect estimates using a Bayesian hierarchical model to generate an average effect for New York, NY. Each heat wave was characterized by its intensity, duration, and timing in the summer. Using a Bayesian hierarchical model, we estimated the effects of each heat wave characteristic on heat wave mortality effects. Results: During the study period, New York City had on average 1.7 heat waves/yr. Mortality increased 6.5% (95% interval: 2.0, 11.2%) during heat waves compared to non-heat wave periods. Relative risk increased 2.8% (1.4, 4.2%) for each 1 of (0.56°C) increase in heat wave intensity and 4.2% (1.1, 7.4%) for each extra day a heat wave lasted. On average, the first heat wave of the year increased mortality 11.7% (7.9, 15.7%), whereas later heat waves increased mortality 1.9% (−2.6, 6.6%). Conclusion: We found increases in mortality during heat waves, with greater impacts from more intense, longer, or earlier heat waves. These findings have implications both for community planners and for researchers estimating potential health effects from climate change.