Typically, a large amount of information is collected during health care research and this information needs to be organised in a way that will make it manageable and to facilitate clear reporting. The Chiropractic Observation and Analysis STudy (COAST) was a cross-sectional observational study that described the clinical practices of chiropractors in Victoria, Australia. To code chiropractic encounters, COAST used the International Classification for Primary Care (ICPC-2) with the PLUS general practice clinical terminology to code chiropractic encounters. This paper describes the process by which a chiropractic-profession-specific terminology was developed for use in research by expanding the current ICPC-2 PLUS system. Methods The coder referred to the ICPC-2 PLUS system when coding chiropractor-recorded encounter details (reasons for encounter, diagnoses/problems, and processes of care). The coder used rules and conventions supplied by the Family Medicine Research Unit at the University of Sydney, the developers of the PLUS system. New chiropractic-specific terms and codes were created when a relevant term was not available in ICPC-2 PLUS. Results Information was collected from 52 chiropractors who documented 4,464 chiropractor-patient encounters. During the study, 6,225 reasons for encounter and 6,491 diagnoses/problems were documented, coded, and analysed; 169 new chiropractic-specific terms were added to the ICPC-2 PLUS terminology list. Most new terms were allocated to diagnoses/problems, with reasons for encounter generally well covered in the original ICPC 2 PLUS terminology: 3,074 of the 6,491 (47%) diagnoses/problems and 274 of the 6,225 (4%) reasons for encounter recorded during encounters were coded to a new term. Twenty-nine new terms (17%) represented chiropractic processes of care. Conclusion While existing ICPC-2 PLUS terminology could not fully represent chiropractic practice, adding terms specific to chiropractic enabled coding of a large number of chiropractic encounters at the desired level. Further, the new system attempted to record the diversity among chiropractic encounters while enabling generalisation for reporting where required. COAST is ongoing, and as such, any further encounters received from chiropractors will enable addition and refinement of ICPC-2 PLUS (Chiro). More research is needed into the diagnosis/problem descriptions used by chiropractors.