AIM: The aim of the present study was to describe trends in periodontal health and oral hygiene using data available from four epidemiological studies on 35-year-olds in Oslo performed from 1973 to 2003. MATERIAL AND METHODS: Periodontal status of randomly selected 35-year-olds was assessed clinically and radiographically. Clinical registrations were based on the Community Periodontal Index of Treatment Needs (CPITN) and the Simplified Oral Hygiene Index. In addition, the proportion of individuals with marginal bone loss was assessed using available orthopantomograms. RESULTS: The proportion of persons with CPITN score 4 (one or more pockets > or = 6 mm) decreased from 21.8% in 1984 to 8.1% in 2003. In addition, the mean number of sextants with deep pockets per person was considerably lower in 2003 than previously. The proportion of persons without recorded bone loss increased from 46% in 1973 to 76% in 2003. An improvement in oral hygiene scores was also observed during this period. CONCLUSIONS: The results suggest that periodontal health and oral hygiene have been improving among 35-year-olds in Oslo during the last 30 years.