The endocytoscopy system (ECS), adapted for clinical use in 2003, is an ultra-high-power magnifying endoscope that allows observations at the cell level. ECS is based on the technology of light-contact microscopy. The most evident use of ECS is for real-time, high-resolution diagnosis of nuclear abnormalities, mainly in patients with esophageal cancer. Up to now, three different types of ECS have been available. This diagnostic tool makes it possible to omit histological examination of biopsy samples in approximately 84% of esophageal squamous cell carcinoma, as evidence for both an increase of cell density and nuclear abnormalities is considered to be convincing proof that a lesion is malignant. Here we describe the features of ECS and the background that led to its development, and review the published literature pertaining to the observation of esophageal neoplasms using ECS.