Cancer of the oral cavity and oropharynx is a major public health problem in Spain. Tobacco and alcohol have been identified as the two major risk factors for oral cancer in most western populations. Other risk factors include diets low in fruits and vegetables, but the impact of dietary habits on the risk of these cancers has never been assessed in Spain. The objective of this study was to elucidate the role of dietary habits in oral and oropharyngeal cancer, a multicentric case-control study was conducted in three areas of Spain (Barcelona, Granada and Sevilla) between 1996 and 1999. Cases were 375 patients (71 women), with incident, histologically confirmed cancer of the oral cavity or oropharynx, and controls were 375 subjects (71 women) admitted to hospitals for conditions unrelated to smoking or alcohol drinking. Data were analysed using multivariate logistic regression procedures. After allowance for education, tobacco and alcohol use, a significant inverse association with the risk of oral and oropharyngeal cancer was found for total consumption of total green vegetables (OR 0.54, 95% CI = 0.34-0.87) and total fruit (OR 0.52, 95% CI = 0.34-0.79) with significant trends in risk. We found that the protective effect of each of these food items was consistently larger among current smokers and among heavy alcohol drinkers, following a multiplicative effect model. In conclusion, this study provides further support to the beneficial effect of high intake of vegetables and fruits on the risk of developing cancers of the oral cavity and oropharynx in Spain, particularly among current smokers and heavy alcohol drinkers.