Aim: to evaluate the left main coronary artery (LMCA) disease in cohort of patients undergoing cardiac catheterization admitted to Cairo university hospitals and As-Salam international hospital, correlate between the left main disease and the patients' risk factors, clinical profile and evaluate the outcome of LMCA disease after surgical treatment, PCI and after diagnostic coronary angiography. Background: LMCA is a serious clinical condition. Despite its low incidence, the prognosis is very poor. There is a renewed interest in percutaneous coronary intervention (PCI) due to improved outcome in patients with high risk for coronary artery bypass grafting (CABG). Methods: This observational prospective study recruited 200 patients in the period from November 2008 to February 2012. These patients were divided equally into group A with significant left main stenosis and group B with significant stenosis of any major epicardial coronary with no significant left main stenosis. All patients were subjected to clinical evaluation, laboratory tests, electrocardiogram, transthoracic echocardiography, coronary angiography and analysis of hospital outcome. Results: Most of patients were males (82%), mean age was (61 ± 9) years. Unstable angina (UA) was the most common presentation in (67%). Hypertension was the most frequent risk factor in (82%). There were 90% of patients associated with other coronary artery disease (CAD). LAD was the most affected artery. There were 6% had left main equivalent and 4% with isolated left main. The mean lumen stenosis was (75 ± 20%) diameter reduction. Most of lesions were distally (64%). It was associated with a lower EF (53.9 ± 14.1%), more dilated LA dimension (3.94 ± 0.56 cm) and LV (5.40 ± 0.8 cm). There were 96% of patients treated surgically and 5% by PCI. The most common major adverse cardiac event (MACE) was the in-hospital myocardial infarction (MI). Conclusion: Coronary angiography is the main tool in LMCAD diagnosis. Left main disease occurs predominantly in males. Most of lesions present distally and the LAD is the most common associated vessel. The LVEDD and LA dimension are wider in the left main patients and EF is lower. There was a significant worsening in the LV systolic and diastolic functions after revascularization. Hypertension (HTN) is the most prevalent risk factor. UA is the most common presentation with dynamic T wave changes in the ECG on admission. CABG is the golden role in treatment. In-hospital MI is the most frequent complication; specially post CABG.