Background
Recently, studies have examined patient and practice factors underlying missed appointments, but less is known about the impact on patient health. People with one or more long-term conditions who fail to attend appointments may be at risk of premature death. This is the first study to examine the effect of missed primary healthcare appointments on all-cause mortality in those with long-term mental and physical health conditions.

Methods
We used a large, nationwide retrospective cohort (N=824,374) extracted from routinely collected general practice data across Scotland which was data linked to Scottish deaths records for patients who had died within a 16-month follow up period. We generated appointment attendance history, number of long-term conditions and prescriptions data for patients. These factors were used in negative binomial and Cox's proportional hazards modelling to examine risk of missing appointments and all- cause mortality.

Results
Patients with a greater number of long-term conditions had an increased risk of missing general practice appointments despite controlling for number of appointments made, particularly among patients with mental-health conditions. These patients were at significantly greater risk of all-cause mortality, and showed a dose-based response with increasing numbers of missed appointments. Patients with long-term mental- health conditions who missed more than two appointments per year had a greater than eight-fold increase in risk of all-cause mortality compared with those who missed no appointments. These patients died prematurely, commonly from non-natural external factors such as suicide.

Conclusions
Missed appointments represent a significant risk marker for all-cause mortality, particularly in patients with mental health conditions. For these patients, existing primary healthcare appointment systems are ineffective. Future interventions should be carried out with particular focus on increasing attendance in these patients.