AbstractA representative sample (n= 8000) was drawn from the population aged 30 years and over, registered as living in Finland. Periodontal disease status was recorded according to the modified Periodontal Treatment Need System (PTNS). Plaque retentions were examined separately. Of the subjects with four or more teeth 3.4% had a healthy periodontal status, while 10.2% of the jaw quadrants were healthy Plaque retentions were found in 96.6% of the subjects and 90.9% of the jaw segments. Periodontal treatment need was calculated in three ways and was 195± 111 (S. D.) min when the calculation was based on WHO recommendations (1978). Number of teeth, age, sex, caries and filling scores, and education explained about 30% of the treatment need when tested by multiple linear regression analysis