A genetic analysis of a female with a 46,XY genotype and typical symptoms of the complete androgen insensitivity syndrome (CAIS) was conducted. The patient was diagnosed with an abdominal tumor due to the presence of a Sertoli cell adenoma in both gonads. Multiple temperature single-stranded conformational polymorphism (MSSCP) and sequence analyses of the androgen receptor gene revealed a c.C2754 > T mutation in exon 6. This mutation, which has not been previously reported, alters a Gln codon to a termination codon (Q798X). This results in the interruption of the amino acid sequence of the androgen receptor within the ligand-binding domain between helices VII and VIII. The truncated form of the receptor is devoid of 123 amino acids at the carboxyl end, a major part of the ligand-binding domain, and the AT2 sequence responsible for the activation of the transcription. It was concluded that the novel c.C2754 > T transition rendered the androgen receptor incapable of both ligand binding and activating the transcription, and was the cause of CAIS in the patient.