Background. Heatwaves have a drastic impact on urban populations, which could increase with climate change. Objectives. The objective of this study was to evaluate, from a public health prevention perspective, new indicators of elderly people's exposure to heat in Paris using satellite thermal images. Methods. We used a time series of 61 NOAA-AVHRR images from August 1 to 13, 2003, to produce thermal indicators of minimum, maximum, and mean surface temperatures, and diurnal temperature amplitude, with different lags between the meteorological data and the health impact. Health data came from a case-control study involving 241 people aged 65 years and over who died in the city of Paris or the nearby suburban area of Val-de-Marne during the August 2003 heatwave, and 241 controls that were matched to cases on age, sex and residential zone. For each person, we integrated the thermal indicators in a conditional logistic regression model, adjusted for age and other potential confounders. We computed odds ratios comparing the 90th and 50th percentiles of the temperature differences between cases and controls for various indicators. Results. Mortality risk was significantly associated with exposure for two indicators: minimum temperatures averaged from August 1 to 13 (OR 2.17, 95% CI 1.14-4.16 for a 0.41 degrees C increase), and minimum temperature averaged on the day of death and the six preceding days (OR 2.24, IC95% 1.03-4.87 for a 0.51 degrees C increase). Conclusions. These results support the influence of night temperatures on the health impact of heatwaves in urban areas. Urban heat exposure indicators based on satellite imagery have the potential to identify areas with higher risk of death, which could inform intervention decisions by key stakeholders.