BACKGROUND: Over the last 5 years, national policy has encouraged general practices to serve populations of >30 000 people (called 'working at scale') by collaborating with other practices. AIM: To describe the number of English general practices working at scale, and their patient populations. DESIGN AND SETTING: Observational study of general practices in England. METHOD: Data published by the NHS on practices' self-reports of working in groups were supplemented with data from reports by various organisations and practice group websites. Practices were categorised by the extent to which they were working at scale; within these categories, the age distribution of the practice population, level of socioeconomic deprivation, rurality, and prevalence of longstanding illness were then examined. RESULTS: Approximately 55% of English practices (serving 33.5 million patients) were working at scale, individually or collectively serving populations of >30 000 people. Organisational models representing close collaboration for the purposes of core general practice services were identifiable for approximately 5% of practices; these comprised large practices, superpartnerships, and multisite organisations. Approximately 50% of practices were working in looser forms of collaboration, focusing on services beyond core general practice; for example, primary care in the evenings and at weekends. Data on organisational models and the purpose of the collaboration were very limited for this group. CONCLUSION: In early 2018, approximately 5% of general practices were working closely at scale; approximately half of practices were working more loosely at scale. However, data were incomplete. Better records of what is happening at practice level should be collected so that the effect of working at scale on patient care can be evaluated.