Paucity of well-defined prognostic molecular markers severely hampers prediction of the clinical course of squamous cell carcinoma (SCC) of oral cavity. The aim of the study was to evaluate the prognostic significance of impairments in the expression of proteins involved in cell cycle regulation and locoregional spread in oral SCC of habitual betel and tobacco chewers. A prospective study was performed in 105 betel and tobacco consumers with oral SCCs during the period 1988-1999, to evaluate the prognostic relevance of impairments in the expression of proteins involved in cell cycle regulation and locoregional spread. Alterations in the expression of p53, pRb, p16, MDM2, p21, and Ets-1 proteins were determined by immunohistochemical analysis in formalin fixed, paraffin embedded tissue sections from oral SCCs. Analysis of multiple molecular biological factors showed overexpression of p53 in 69/105 (66%) cases, MDM2 in 72/105 (69%) cases, p21 in 57/105 (54%) cases and Ets-1 in 64/105 (61%) cases. Loss of pRb was observed in 58/105 (55%) cases and p16 loss was observed in 72/105 (69%) cases. Interestingly, multivariate analysis revealed loss of pRb as the most significant predictor of advanced tumour stage [P=0.001; Odd's Ratio (OR)=3.5] and overexpression of Ets-1 protein was an independent risk factor for lymph node metastasis (OR: 10.1; P<10(-6)). Multiple logistic regression models showed that pRb loss [Hazard's Ratio (HR): 3.93] and p53 overexpression (HR: 2.97) may serve as adverse prognosticators for disease free survival of the patients. The data demonstrate multiple impairments in p53/MDM2/p21/Ets-1 and p16/pRb pathways in betel and tobacco related oral tumourigenesis.