An instrument for intraoperative sensing of surgeons' hand tremor during vitreoretinal microsurgery has been developed. The instrument uses inertial sensing to detect tremor in six degrees of freedom. Instrument tip velocity is computed using the sensor data. The displacement amplitude of the tremor is then approximated analytically by modeling the velocity as sinusoidal. The instrument presently estimates oscillations at physiological tremor frequencies with error of less than 7%.