Objectives: To describe an outbreak of adenovirus, type 30, in a neonatal int ensive care unit (NICU). Study design: This was a retrospective, observational s tudy. Results: An outbreak of adenovirus infection occurred in an NICU. It laste d 6 months and involved 21 of 333 (6.3% ) infants. The introduction of infectio n control measures controlled the outbreak; however, premature discontinuation o f the measures resulted in a second wave of cases. The virus caused pneumonia in 7 infants, conjunctivitis in 7 infants, pneumon ia and conjunctivitis in 1 infant, and upper respiratory tract illness in 1 infa nt. Infection was asymptomatic in 5 infants. Six infants died. Death was associa ted with the presence of pneumonia (P = .0001), administration of steroids (P = .003), and mechanical ventilation (P = .02). Investigation into the origin of th e outbreak suggested that the virus may have been introduced and spread during o phthalmologic procedures. Conclusions: Adenovirus type 30 can cause severe disea se among premature infants in an NICU. Infants with severe bronchopulmonary dysp lasia requiring mechanical ventilation are more likely to have development of ad enovirus pneumonia and die. Standard infection control measures are effective in controlling an outbreak. Ophthalmologic procedures continue to be a potential s ource of adenovirus outbreaks. Objectives: To describe an outbreak of adenovirus, type 30, in a neonatal int ensive care unit (NICU). Study design: This was a retrospective, observational study. Results: An outbreak of adenovirus infection occurred in an NICU. It laste d The introduction of infectio n control measures controlled the outbreak; however, premature discontinuation of the measures resulted in a second wave of cases. The virus caused pneumonia in 7 infants, conjunctivitis in 7 Infants, pneumon ia and conjunctivitis in 1 infant, and upper respiratory tract illness in 1 infa nt. Infection was asymptomatic in 5 infants. Six infants died. Death was associa ted with the presence of pneumonia (P = .0001), administration of steroids (P = .02). Investigation into the origin of th e outbreak suggested that the virus may have been introduced and spread during o phthalmologic procedures. Conclusions: Adenovirus type 30 can caus erous diseae se among premature infants in an NICU. Infants with severe bronchopulmonary dysp lasia requiring mechanical ventilation are more likely to have development of ad enovirus pneumonia and die. Standard infection control measures are effective in controlling an outbreak. Ophthalmologic procedures continue to be a potential s ource of adenovirus outbreaks.