A single nucleotide polymorphism (SNP) located at position-1 in the Kozak sequence of the CD40 gene has been associated with the development of GD in Caucasian and Koreans. This study investigated possible associated between CD40 SNP and the development of GD in a Taiwanese population. To do this, we enrolled 215 Taiwanese patients with GD and 141 controls from the Endocrine Clinic of Kaohsiung Medical University Hospital. This study investigated the association between gene polymorphism and relapse of hyperthyroidism after the discontinuation of medication in three GD patient groups based on time to relapse and a control group, and compared clinical and laboratory data of patients regrouped in three CD40 SNP genotypes. No significant difference in allele or CD40 SNP genotype frequency was observed between patients with GD and control subjects (P = 0.859 and P = 0.959, respectively). Furthermore, we analyzed the distribution of CD40 genotypes and three groups based on time to relapse after drug withdrawal. The cutoff points were 9 months, 9 months to 3 years, and more than 3 yr in subgroups of patients with GD divided by clinical and laboratory variables. Although no significant genotype-phenotype associations were found, the T allele and TT genotype frequency was significantly smaller in GD patients who had developed the disease before 35 years old than those who developed it after 35 years old (x (2) = 6.272, P = 0.043) (TT + CT v.s. CC, x (2) = 4.951, P = 0.030). These findings suggest that this CD40 gene polymorphism is not associated with GD in Taiwan and is, therefore, not contributing to susceptibility to the disease there.