Background. Governments are increasing pressure on GPs to provide better services to their patients without giving consideration or due recognition to the impact of those initiatives on their already heavy workload. Objective. This pilot study aimed to measure accurately the impact of case mix on general practice workload. Method. The general practice-specific care category (GP-SCC) model was developed and applied to a random sample of patients who attended a four-doctor suburban practice four or more times between July 1995 and June 1997. Results. The random sample comprised 245 patients (126 males, 119 females) out of a total practice population of ∼4000. The mean patient age was 42.7 years (CI 39.6–45.8; range: 0–95). The mean patient consulted 10.70 times (CI 9.62–11.77) and discussed 13.19 health problems (CI 11.74–14.63), which equated to 1.20 problems per consultation (CI 1.17–1.23). The ambulatory case mix concept allowed the development of the GP-SCC model—defined as GP-SCC 1, acute/self-limiting problems and preventive care; GP-SCC 2, primarily chronic health problems; GP-SCC 3, psychological problems in conjunction with up to two other problem categories; and GP-SCC 4, a combination of four or more problem categories. GP-SCC 1 comprised 31.1% of patients (CI 29.1–35.1), accounting for 25.6% of visits (CI 24.0–27.3) and 21.9% of all problems encountered (CI 20.5–23.3); GP-SCC 2 comprised 16.7% of patients (CI 10.6–19.6), accounting for 10.6% of visits (CI 9.5–11.9) and 9.9% of all problems encountered (CI 8.9–11.0); GP-SCC 3 comprised 7.1% of patients (CI 4.4–11.2), accounting for 7.8% of visits (CI 6.8–8.9) and 7.7% of all problems encountered (CI 6.8–8.7); and GP-SCC 4 comprised 42.0% of all patients (CI 35.8–48.2), accounting for 56.0% of all visits (CI 54.2–57.8) and 60.5% of all problems encountered (CI 58.8–62.2). Conclusions. The GP-SCC model, built on the ambulatory case mix concept, is a useful tool to analyse the morbidity of practice populations, and has a good predictive value in terms of a practice' workload.