Article dans une revue: Job insecurity can have wide-ranging consequences outside of the labour market. A 1999 rise in the French layoff tax paid by large private firms when they laid off older workers made younger workers less secure; this insecurity reduced their fertility by 3.7 percentage points (with a 95% confidence interval between 0.7 and 6.6 percentage points). Reduced fertility is only found at the intensive margin: job insecurity reduces family size but not the probability of parenthood itself. Our results also suggest negative selection into parenthood, as this fertility effect does not appear for low-income and less-educated workers.