As the quality of clinical information contained in referral letters for specialist care may determine the initial decisions as to appropriate treatment for patients, it is important that this information is objective and accurate. The use of a standardised questionnaire for this purpose improves the quality of information received, but it is not known how accurate this information is if used in the decision-making process for treatment planning. The aim of this study was to compare the clinical assessment data derived from a standardised questionnaire used by referring patients to a specialist periodontal unit. Equivalent data recorded by dentists and periodontists were compared to establish whether the data were consistently reproducible, and therefore usable for deciding on the appropriate initial phase of treatment for patients. Data from 50 patients referred for periodontal treatment planning and specialist care in which the questionnaires from the general dental practitioner and the subsequent periodontal assessment were available were compared. All of the patients were medically healthy and were not taking any long-term medication. The patients were selected based on the retrospective availability of equivalent clinical data from the questionnaires and consultation in the periodontal department at the Eastman Dental Hospital, London. The equivalence or disparity in the identification of different cofactors, and the community periodontal index of treatment need (CPITN) (basic periodontal examination, BPE) scores recorded by referring dentists (GDP), and periodontists (EDH, Eastman Dental Hospital) were annotated and compared. A level of equivalence of over 50% of assessments was demonstrated between referring dentists and periodontists in the variables of oral hygiene, smoking, bleeding on probing and restorative factors, as well as in the recorded scores of the CPITN (BPE) screening system. It can be concluded that the use of questionnaires for referral for specialist services is useful to not only improve and standardise the quality and extent of the relevant clinical information received, but may also be a valuable resource that may be used in the initial decision-making process for screening patients to the appropriate level of periodontal care. However, the limitations of this observational study preclude drawing any definitive conclusions in the absence of a more carefully controlled study designed specifically to overcome these limitations.