397 children aged 12-17 years from different schools were divided into two groups. Group I comprised 192 children from private schools in Athens and Group II comprised 205 children from state schools of an industrial area in Piraeus. They were also subgrouped according to their socioeconomic class. They were interviewed with regard to their oral health habits, frequency of dental visits, etc., and subjected to clinical examination using the criteria and indices described by Silness & Löe and Löe & Silness. Stepwise regression analysis was used in the statistical evaluation of factors related to GI and Pl I. The following factors were found to be statistically significant in relation to GI: socioeconomic class, toothbrushing frequency, sex, and group examined. For Pl I statistically significant factors were found to be: age, group examined, and sex. All other variables were not significantly correlated to GI and Pl I.