The aim of this study was to determine whether the differential assessment of epithelial proliferation is useful to diagnose premalignant fields and assess the risk of multiple tumours.We analysed 83 oral carcinomas with associated non-tumour epithelium classified as distant or close according to its distance (> or <1 cm) from the invasion point, and as squamous hyperplasia, mild, moderate, severe dysplasia or carcinoma in situ. Twenty-five healthy oral mucosa samples were used as controls. An immunohistochemical technique was applied using Mib-1. Ki-67 in premalignant epithelium was assessed in basal layer, parabasal layer, medium and upper third.Parabasal expression was significantly higher or showed a tendency to be higher in close and distant epithelia with any histological grade than in the controls. Parabasal Ki-67 significantly differed between distant epithelia associated with multiple vs single tumours (P < 0.001) and between distant epithelia associated with multiple tumours vs controls (P < 0.001). This difference was not observed between distant epithelia associated with single tumours and controls (P = 0.175). The cut-off point that differentiated epithelia associated with multiple tumours was >50% of Ki-67 + parabasal cells in distant epithelia, which yielded 0.88 sensitivity and 0.79 specificity.The concept of a precancerous field may be linked to an increase in the proliferative activity of parabasal cells.