To clarify the associations of the egfr CA repeat polymorphism with asthma and its severity, we examined 579 Japanese asthmatics and 232 control subjects. The number of CA repeat ranges from 9 to 24. Asthmatic patients had a significantly higher incidence of having shorter alleles (<==16 CA repeats) compared with control subjects (p < 0.05). The most severe asthmatic patients have the highest frequency of short alleles (p < 0.05). In addition, subjects treated with leukotriene modifiers had higher incidence of having shorter allele compared to those without it (p < 0.01). Thus, the egfr CA repeat polymorphism is associated with the susceptibility and the severity of asthma.