The aim of this study was to investigate whether cigarette smoking had any impact on the clinical outcomes 1 year after active periodontal treatment. Eligible for the study were 5680 individuals 20-85 years, referred to the specialised clinic for periodontal treatment at Gävle County Hospital between the years of 1980 and 2015. Before examination, all individuals filled in a questionnaire regarding their medical health, medication and smoking habits.