While the presence of CYP11A1 (P450SCC, cholesterol side-chain cleavage enzyme) has been well established in the brain of rodents, limited information is available on CYP11A1 expression in human brain. In both species, little is known regarding postnatal changes or sex specific differences in cerebral CYP11A1 expression. In the present study, we used a sensitive competitive reverse transcriptase polymerase chain reaction (RT-PCR) assay to quantify the amount of CYP11A1 mRNA in a large number of human brain tissue specimens obtained at neurosurgery. CYP11A1 mRNA is expressed approximately 200 times lower in the temporal lobe, frontal lobe and hippocampus than in adrenal tissue, known for high CYP11A1 mRNA expression. During childhood CYP11A1 mRNA concentrations in the temporal lobe increase markedly and reach adult levels at puberty. CYP11A1 mRNA is significantly higher in the temporal and frontal lobe cortex of women than in that of men. Our data demonstrate for the first time an age and sex dependent expression of CYP11A1 mRNA in the human brain.