Patients with a karyotype of 45,X (monosomy X) normally display a female phenotype. However, in some rare cases, monosomy X is associated with maleness. Here we describe a case of a male with a 45,X karyotype and primary infertility, which prompted molecular investigation of the sex-determination gene SRY.Karyotyping was performed by GTG-banded chromosome analysis. The presence and location of SRY was investigated using PCR and FISH, respectively.PCR confirmed the presence of the SRY gene while FISH analysis demonstrated its location on the p arm of chromosome 13. These findings demonstrate that autosomal retention of SRY can be sub-microscopic and emphasize the importance of PCR and FISH in the genetic workup of the monosomic X male.