Aim: Our aim was to investigate the characteristics, treatment and prognosis of patients with myocardial infarction (MI) treated outside a cardiology department (CD), compared with MI patients treated at a CD. Methods: A cohort of 1310 patients diagnosed with MI at eight Swedish hospitals in 2011 were included in this observational study. Patients were followed regarding all-cause mortality until 2018. Results: A total of 235 patients, exclusively treated outside CDs, were identified. These patients had more non-cardiac comorbidities, were older (mean age 83.7 vs. 73.1 years) and had less often type 1 MIs (33.2% vs. 74.2%), in comparison with the CD patients. Advanced age and an absence of chest pain were the strongest predictors of non-CD care. Only 3.8% of non-CD patients were investigated with coronary angiography and they were also prescribed secondary preventive pharmacological treatments to a lesser degree, with only 32.3% having statin therapy at discharge. The all-cause mortality was higher in non-CD patients, also after adjustment for baseline parameters, both at 30 days (hazard ratio (HR) 2.28; 95% confidence interval (CI) 1.62–3.22), one year (HR 1.82; 95% CI 1.39–2.36) and five years (HR 1.62; 95% CI 1.32–1.98). Conclusions: MI treatment outside CDs is associated with an adverse short- and long-term prognosis. An improved use of percutaneous coronary intervention (PCI) and secondary preventive pharmacological treatment might improve the long-term prognosis in these patients.