A liquid crystal display (LCD) with a built-in touch screen includes: a first substrate including a sensor area having a plurality of photosensors; a second substrate positioned over the first substrate, and including a color filter, a light receiving portion, and a transparent electrode layer and a front polarizing plate; an LCD panel including a liquid crystal layer interposed between the first and second substrates; a touch screen driver circuit to measure a capacitance variation sensed through a first sensing line connected to the transparent electrode layer and to calculate a touch area using optical information sensed through a second sensing line connected to the photosensors when a contact object is in contact with the LCD panel, and to output position information of the contact object, sensed by determining whether a touch occurs and whether a multi-touch occurs using the capacitance variation and the touch area.