Evidence of field change in oral cancer was assessed using quantitative cytomorphometric analysis of smears taken from normal buccal mucosa in oral cancer-free patients. The nuclear areas (NA) and cytoplasmic areas (CA) were calculated using a semi-automatic image analysis system. A statistically significant reduction in CA (p = 0.002) but no change in NA was observed for the oral cancer group. This change occurred irrespective of tobacco and alcohol usage. We believe this to be the first evidence for true field change since Slaughter's original hypothesis in 1946.