Esophageal squamous cell cancer (ESCC) is common in the developing world, and is the leading cancer diagnosis at Tenwek Hospital in southwestern Kenya. The investigators long-term goal is to understand the pathogenesis and risk factors for ESCC in Kenya, and to establish effective screening and prevention programs. The investigators hypothesize that asymptomatic esophageal squamous dysplasia (ESD) is common in their region, and the current protocol is designed to determine the prevalence of ESD in residents of southwestern Kenya.

The prevalence of esophageal squamous dysplasia will be determined after evaluating pathology reports from unstained lesions and normal biopsies after staining with Lugol's iodine.

Inclusion Criteria:

• Age ≥ 20 years
• No dysphagia (subjects will be asked "do you have trouble swallowing food or water? Do they get stuck inside after you swallow?" in their primary language

Exclusion Criteria:

• Cardiac, respiratory, or metabolic disease that would increase the risk of endoscopy: history of myocardial infarction, arrhythmias, chronic obstructive pulmonary disease, diabetes, allergy to lidocaine.
• Unable or unwilling to provide informed consent.

Adult Asymptomatic subjects residing within a 50 kilometer radius of Tenwek Hospital