A field experiment was conducted in France to evaluate the impact of health information on fish consumption. A warning revealed the risks of methyl mercury contamination in fish and gave consumption recommendations. A difference-in-differences estimation shows that this warning led to a statistically significant but relatively weak decrease in fish consumption. Consumption of the most contaminated fish did not decrease despite advice to avoid consumption of these fish. Accompanying questionnaires show that consumers imperfectly recall the fish species quoted in the warning. The results suggest a relatively poor efficacy of a complex health message, despite its use by several national health agencies. Copyright 2009, Oxford University Press.