Parainfluenza viruses (PIV) are single-stranded RNA viruses belonging to the paramyxovirus family. These viruses cause endemoepidemic upper respiratory tract disease (nasopharyngitis, laryngitis and tracheitis) which may lead to bronchiolitis and pneumonia in young children. Parainfluenza viruses can also cause serious lower respiratory tract disease with repeat infection especially among the elderly, and among patients with compromised immune systems. They are spread from respiratory secretions through close contact with infected persons or contact with contaminated surfaces or objects. PIV are divided into four types: PIV1 to 4. They share antigenic cross-reactivity but tend to cause diseases of different severity. The most distinctive clinical feature of PIV-1 and PIV-2 is croup (i.e., laryngotracheobronchitis); PIV-1 is the leading cause of croup in children, whereas PIV-2 is less frequently detected. Both PIV-1 and -2 can cause other upper and lower respiratory tract illnesses. PIV-3 is more often associated with bronchiolitis and pneumonia. PIV-4 is infrequently detected, possibly because it is less likely to cause severe disease. The incubation period for PIVs is generally from 1 to 7 days. The detection of PIV-specific IgG antibodies is suggestive of past or recent infection with PIV. However, cross-reactivity between PIV types is possible. A fourfold rise or drop in titre is generally thought to signify acute infection. The detection of PIV-specific IgM antibodies indicates current or recent infection with the virus.