BACKGROUND: In the UK, the majority of primary care contacts are uncomplicated. However, safety incidents resulting in patient harm occur, such as failure to recognise a patient's deterioration in health. AIM: We aimed to determine patient and healthcare factors associated with potentially missed deterioration. DESIGN AND SETTING: A cohort of patients registered with English CPRD general practices between 01-04-2014 and 31-12-2017 with linked hospital data. METHODS: We defined a potentially missed deterioration as a patient, seen in primary care by a GP in the three days before hospitalisation, having a self-referred admission. We used generalised estimating equations to investigate factors associated with odds of a self-referred admission. We investigated all diagnoses and subsets of commonly reported missed conditions. RESULTS: There were 116,097 patients who contacted a GP three days prior to an emergency admission. Patients with sepsis or urinary tract infections were more likely to self-refer, adjusted odds ratio 1.10 95%CI(1.02-1.19) and 1.09 (1.04-1.14) respectively. GP appointment durations were associated with self-referral. On average, a 5-minute increase resulted in 10% decrease in odds of self-referred admissions, 0.90 (0.89-0.91). Patients having a telephone (compared with face-to-face) consultation 1.13 (1.09-1.16), previous health service use and health status were also associated with self-referred admission. CONCLUSIONS: Differentiating deterioration from self-limiting conditions can be difficult for clinicians, particularly in patients with sepsis, UTI or with long-term conditions. Our findings supports the call for longer GP consultations and cautions reliance on telephone consultations in primary care; however, research is needed to understand the underlying mechanisms.