The present invention relates to a method for determining a state of tissue sealing during a tissue sealing process. According to the disclosed method, an optical probe beam is used to irradiate a tissue region. A signal indicative of optical scattering in the tissue region is generated from a portion of the optical probe beam that has passed through or been returned by the tissue region. The onset of tissue sealing is indicated by the successive occurrence in time of a turning point and a point of inflection in the optical scattering signal. An energy-based tissue sealing or tissue-cutting device for use in accordance with the method is also disclosed.