Background. The main cause of acute coronary syndrome (ACS) is coronary artery obstruction due to atherosclerotic plaque growth or thrombus formation secondary to plaque rupture or erosion. However, there is a subgroup of patients with signs and symptoms suggestive of ACS but without relevant coronary artery obstruction on coronary angiography. This population is defined as myocardial infarction with non-obstructive coronary arteries (MINOCA). The present study analyzes the clinical features and outcomes of very young patients with a diagnosis of MINOCA. Method. Nested case-control study of ≤40-year-old patients referred for coronary angiography due to clinical suspicion of ACS. Patients were divided into three groups: patients with obstructive coronary artery disease (CAD), patients diagnosed with MINOCA, and controls with non-coronary artery disease. Results. Of 19,321 coronary angiographies performed in our center in a period of 10 years, 408 (2.1%) were in patients ≤40 years old, and MINOCA was identified in 32 (21%) patients. The cardiovascular risk factors for obstructive CAD and MINOCA were very similar. The incidence of major adverse cardiovascular events (MACE) at follow-up was significantly higher in the MINOCA (HR 4.13 (95%CI 1.22–13.89) and obstructive CAD (HR 4.59 (95%CI 1.90–10.99) patients compared to controls. Cocaine use HR 14.58 (95%CI 3.08–69.02), family history of CAD HR 6.20 (95%CI 1.40–27.43), and depression HR 5.16 (95%CI 1.06–25.24) were associated with a poor outcome in the MINOCA population. Conclusion. Very young patients with MINOCA had a poor prognosis at long-term follow-up, similar to patients with obstructive CAD. Focusing efforts on secondary prevention is essential in this population.