Purpose: The aim of this study was to explore the dental functional status of a Southern Vietnamese adult population using a new quantitative- and qualitative-based classification system. Materials and Methods: The sample consisted of 2,809 dentate subjects aged >= 20 years from urban and rural areas of Southern Vietnam. Dentitions were classified by a dichotomized five-level step-by-step branching hierarchy reflecting functionality. Cut-offs were as follows: level I (dentition level) = 1 tooth present in each arch, level II (arch level) = 10 teeth in each arch, level III (anterior region) = all 12 anterior teeth present, level IV (premolar region) = >= 3 premolar posterior opposing pairs (POPs) present, and level V (molar region) = 1 molar POP bilaterally. Results: Of the 2,809 subjects, 44% met all criteria for a functional dentition and 16% met none. Of subjects meeting level II, 81% had a complete anterior region, 74% had a sufficient premolar region, and 66% had a sufficient molar region. For subjects not meeting level II, these figures were 9%, 15%, and 8%, respectively. For patients meeting level II who were between 20 and 35 years of age, a mean 29.2 ± 2.4 teeth and 7.9 ± 2.1 POPs were present; subjects 65 years of age and older had a mean 25.6 ± 3.2 teeth and 5.9 ± 2.1 POPs. For patients not meeting level II, these numbers were 18.6 ± 2.9 teeth and 3.1 ± 1.8 POPs and 12.8 ± 5.4 teeth and 0.9 ± 1.4 POPs for 20- to 35-year-olds and those 65 years of age and older, respectively. Intraclass correlation coefficients for number of teeth and POPs showed fair to good group homogeneities. Conclusions: The World Health Organization goal of retaining at least 20 teeth throughout life is not achieved in Southern Vietnam; above the age of 44, less than 75% of subjects presented with 20 or more teeth. The presented classification system is a useful framework for mapping the functionality of dentitions by applying additional criteria for dental regions.