Adenoviruses have been detected in raw sewage throughout the world and are associated with a number ofhuman illnesses but their occurrence and pathogenicity have not been well studied. A risk assessment approach was used to determine their significance as a waterborne pathogen. There arc 47 types of adenoviruses and the diseases resulting from infections include conjunctivitis, pharyngitis, pneumonia, acute and chronic appendicitis, cxanthematous disease, bronchiolitis, acute respiratory disease, and gastroenteritis (types 40 and 41). Adenovirus is considered to be only second to rolavirus in terms of its significance as a pathogen of childhood gastroenteritis. Adenovirus infections are usually acute and self-limiting with a greater severity of illness occurring in the immunocompromised (e.g. AIDS patients and transplant recipients). They are repofled to be more resistant to inactivation by UV than enteroviruses and are sometimes detected at higher levels in polluted waters. There are documented outbreaks of conjunctivitis due to adenovirus types 3 & 4 associated with swimming in contaminated recreational waters. Based on the data obtained from human dose-response studies, the exponential model [Pi = l -exp(-rN); r = 0.4172] was chosen for this risk assessment. Annual risks of infection in drinking water for adenovirus at average levels of 1/1,000L to 1/100L ranged from 8.3/10,000 to 8.3/1,000, respectively. Using monitoring data from a recreational water, risks were calculated to be as high as 1/1,000 for a single exposure.