Doctors said an MRI scan on Sunday had revealed the formation of a "right transversesinus venous thrombosis" - a clot in the vein behind Mrs Clinton's right ear in the space between the brain and the skull.
"It did not result in a stroke, or neurological damage," said Dr Lisa Bardack and Dr Gigi El-Bayoumi, who were treating Mrs Clinton at New York's Presbyterian hospital.
The secretary of state was said to be in good spirits and"engaging with her doctors, herfamily, and her staff," added thedoctors in a statement.