Parainfluenza viruses are a major cause of hospitalization for respiratory illness in children. The spectrum of clinical illness associated with infection due to parainfluenza type 4 virus has not been well defined. It is technically difficult to isolate the virus in tissue culture, and because illness is generally reported to be mild, in many cases, patients may not seek medical attention. We describe a series of 10 children with parainfluenza type 4 virus infection who were seen at the Montreal Children's Hospital between 1988 and 1992. There were five males and five females whose average age was 29.7 months. Infection was associated with symptoms of bronchiolitis or pneumonia in 5 children, paroxysmal coughing in 3 infants, apnea in 1 newborn, and aseptic meningitis in 1 child. Hospitalization was required for 8 of the 10 children. It appears that infection with parainfluenza type 4 virus may be more common than previously recognized, and it may be associated with more severe infections.