INTRODUCTION: France was affected in early August 2003 by a heat wave with an exceptional health impact. Many studies on mortality were conducted but few data are available on morbidity. The objectives of this study were to describe the impact of the 2003 heat wave in the general population of elderly people and to determine individual factors associated with morbidity. METHODS: A cross-sectional study nested in two prospective cohorts, the PAQUID and the Three-City (3C) studies, was performed. The sample included 2295 subjects from the general population, aged 67 and over who were interviewed by a phone questionnaire to complete data available in the database of the two cohorts. Two variables assessing morbidity (felt by the person and objectively observed) were created. Relationship between morbidity and individual factors were explored in univariate analyses; then multiple logistic regressions were conducted. RESULTS: During the heat wave, 8.8% of the subjects felt a deterioration of their health, and 7.8% declared an objective morbid outcome. In the univariate analyses, many factors were associated with morbidity. After multiple adjustments, few associations were still observed but some factors were associated with a decreased risk (presence of a bathroom, dressing lighter than usually) or an increased risk (stopping usual activities, presence of chronic diseases). CONCLUSION: This study showed a non-negligible impact of the 2003 heat wave in term of felt and objective morbidity. Several individual factors were shown to be associated with morbidity and should be taken into account for the elaboration of prevention plans.