There is widespread, unexplained variation in activity and outcome between general practices.

To explore the relationship between practice size and participation in optional activities, including the Quality and Outcomes Framework (QOF).

Cross-sectional analyses of routinely available data on practice characteristics, QOF performance and optional activities including undergraduate teaching, postgraduate training, research, enhanced clinical data collection and service development.

All 1031 general practices were located in mainland Scotland.

The most popular optional activity was undergraduate medical teaching, which involved 41% of all general practices. About a third of practices took part in postgraduate general practitioner training (29%), research (33%), enhanced clinical data collection through the Scottish Programme for Improving Clinical Effectiveness (31%) and the activities of the Scottish Primary Care Collaborative (33%). The most important driver of the number of activities undertaken by a practice is size with single handed, small and medium sized practices all undertaking a significantly lower number of activities than larger practices (P < 0.001). Deprivation had no overall effect, but was associated with lower rates of participation in postgraduate training. The average number of points achieved in the QOF ranged from 961 by the 18% of practices taking part in no optional activities, to 973 by 29% of practices taking part in one activity, 984 by 25% of practices taking part in two activities and 985 in 28% of practices taking part in three or more activities. Single handed practices in urban areas taking part in three or more additional activities had similar QOF point totals to larger practices taking part in three or more activities, and achieved 44 more QOF points than urban single-handed practices taking part in less than two additional activities.

Practice size is strongly related to participation in optional activities. There is a small but significant relationship between the practice size and number of QOF points achieved by practices taking part in less than two additional activities. Participation in optional activities is a possible indicator of cultural and organisational factors within practices, which constrain the volume and quality of services, which they are able to provide.