The cat cry (cri du chat) syndrome is a rare congenital anomaly due to partial deletion of the short arm of the No. 5 chromosome. Since the first report of Lejeune et al, in 1963, nearly 400 cases have been reported. However, the syndrome with a ring chromosome is still very rare and only 10 cases were reported up to 1988, since the first report of Rohde and Tompkins in 1965. To investigate the chromosomal changes in the patients of cat cry syndrome, a chromosomal study was carried out on 10 cases of cat cry syndrome from 5,870 cases submitted to the Laboratory of Cytogenetics, National Taiwan University Hospital from Nov. 1968 through Apr. 1988. These ten cases included 3 males and 7 females (M:F = 1:2.3) aged 2 days to 18 months with an average of 5.5 months. The most common clinical features are: cat-like cry, growth failure, microcephaly with mental retardation, round face with facial abnormalities including hypertelorism, downward slanting palpebral fissures, micrognathia and low-set ears, and simian crease. Laryngomalacia or underdevelopment of the larynx may be a factor causing the cat-like cry. On chromosome analysis, 8 out of these 10 cases showed the usual simple deletion of the short arm of the no. 5 chromosome, and the other 2 cases revealed ring chromosome including a case of pure ring chromosome([(4, XY, r (5)] and a case of mosaicism with one ring chromosome, 2 ring chromosomes and simple deletion of the short arm of the No. 5 chromosome.(ABSTRACT TRUNCATED AT 250 WORDS)