The present epidemiologic dental caries study indicates a high number of decayed surfaces (mean, 13.5±11.8 (SD)) in a Portuguese population of 30- to 39-year-olds from Porto. The most influential determinants for variation in carious surfaces were oral hygiene, gender, salivary buffer capacity, and missing teeth. By entering the most influential independent variables in a final multiple classification analysis, the total explained variance in carious surfaces was 27%. A comparison with results from a similar Norwegian dental health study showed that the biologic factors of importance for number of carious surfaces were the same, whereas the sociocultural determinants differed.