Purpose: To evaluate if periodontists are coherent in their judgement and treatment decisions of patients with different periodontal conditions, and to compare them with general dental practitioners' (GDPs) findings. Materials and Methods: Eighty-six periodontists participated in a questionnaire study based on four patient cases: (a) generalised bone loss but minimal signs of inflammation (well-maintained); (b) generalised bone loss and signs of inflammation (periodontitis); (c) negligible bone loss and minimal signs of inflammation (healthy); and (d) negligible bone loss but with signs of inflammation (gingivitis). Periodontists had the option to judge each patient as healthy or diseased, propose a diagnosis, evaluate treatment needs, propose a treatment plan and assess the prognosis. Comparison between periodontists considered: (a) level of experience and (b) judgement of each patient case as healthy or diseased. Periodontists were additionally compared to a previous sample of GDPs (n = 74). Results: Periodontists' response rate was 77%. The diagnostic judgement of the four patient cases showed rather large variation both among periodontists and GDPs. Periodontists' intention to treat and prognostic assessment depended on their judgement of each patient, as healthy or diseased (p 0.05). GDPs intended to treat three out of four patient cases (except periodontitis case) more often and were more pessimistic in their prognostic assessment of patients with negligible bone loss (p 0.05), comparing to periodontists. Conclusions: Both periodontists and GDPs are defining periodontal health and disease differently, which affects treatment decisions and prognostic assessment. There is a need to define periodontal health and disease more precisely, in order to improve coherence in judgement. Keywords: clinical decision-making, gingivitis, periodontal diseases, periodontitis, specialists